How to Fix Outlook OST File cannot be Opened on Windows 10/11

The OST file cannot be opened error indicates that Outlook cannot read or access your offline data (.ost) file. This error can prevent you from accessing the mailbox items, thus disrupting your workflow. There are several internal and external factors that can lead to this issue. In this guide, we’ll discuss why this error occurs and share some effective solutions to fix it.    

Why Outlook OST File cannot be Opened Error Occurs?

There are several reasons that can prevent Outlook from opening an OST file. Let’s take a look at some common ones:

• Corruption or inconsistencies in the OST file
• OST file is inaccessible or becomes orphaned due to profile deletion
• OST file has reached its defined size limit
• Some Outlook processes are running in the background, locking the OST file
• Outlook is running in Compatibility Mode
• Outlook or Windows lacks the latest updates
• Corrupted or damaged Office installation files
• Errors on disk storing the OST file
• Faulty COM add-ins are interfering with Outlook’s functionality
• Antivirus or other security software has locked the OST file while scanning

Quick Check: Is Outlook still Running in the Background?

Outlook processes running in the background keep the OST file locked. When you launch a new instance of Outlook, it is not able to access the file, triggering this error. So, first check whether any Outlook process is running in the background. For this, open Task Manager by pressing Ctrl + Shift + Esc. If you find Outlook.exe isrunning in the Processes tab, close it by clicking End Task.

After closing the Task Manager, open your email client again. If you still encounter the error, follow the methods mentioned below.  

Methods to Resolve Outlook OST File cannot be Opened Error on Windows 10/11

Below are some simple yet effective fixes to resolve this error.

Method 1: Disable Faulty or Conflicting Add-ins

Third-party add-ins are installed to enhance Outlook’s functionality. If there are any outdated or faulty add-ins, they may interfere with your application’s functionality. To check if any add-in is causing this error, you can start the application in Safe Mode by following these steps:

• Press the Windows + R keys.
• Type Outlook.exe /safe and press the Enter key or click OK.

If it opens without the error, this means a faulty add-in is likely causing the problem. You can disable the add-ins by following these steps:

• Navigate to the File tab and then go to Options.
• In the Outlook Options window, click on Add-ins.
• In the Manage field at the bottom, make sure the COM Add-ins option is selected and then click Go.

• On the COM Add-ins window, unselect all add-ins and click OK.
• Close Outlook and open it in normal mode.

To identify the faulty add-in, enable one add-in at a time. Once you find the add-in that is causing the problem, you can remove it permanently.

Method 2: Update Outlook (MS Office) and Windows

Microsoft regularly releases updates for its products, such as Windows, MS Office, and others to improve their performance, add new features, and fix bugs, glitches and issues. If your MS Office (Outlook) program or Windows are not updated, then they may develop bugs or glitches that can cause various issues. So, make sure the latest updates for Outlook and Windows are installed.

If your email client is not opening, then you can open any MS Office program to install the updates. Here’s how:

• Open Word or Excel.
• Go to File > Account (or Office Account).
• Under Office Updates, select Update Options > Update Now.

You can download and install Windows updates to get the latest bug fixes and updates for MS Office, including Outlook.

Once finished, restart your system and open Outlook to check if the issue is resolved.

Method 3: Reset Navigation Pane

Navigation Pane stores the folder hierarchy, shortcuts, and view preferences in an XML configuration file (profile-name.xml). If this configuration file is damaged or corrupted, Outlook fails to recognize and load your OST file during startup. You can fix this issue by resetting the Navigation Pane. To do this,

• Open the Run utility (press Windows + R keys)
• Type outlook.exe /resetnavpane. 
• Hit the Enter key or click OK.

Method 4: Repair Outlook

If your Outlook program files are damaged or corrupted, it can cause various issues and errors, including the OST file cannot be opened error. In such a case, repairing the program can resolve the problem. Follow these steps:

Note: Make sure all the MS Office applications are closed.

• On your system, go to Control Panel > Programs and Features.
• Select Microsoft Office from the list and click Change.

• Two repair options will appear: Quick Repair and Online Repair.
• Choose the Quick Repair option and then click Repair.

If the error persists, choose the Online Repair option and then complete the repair wizard.

Method 5: Disable Outlook Compatibility Mode

Compatibility mode is a feature in Windows that allows older programs to run on newer Windows’ versions. However, running Outlook in this mode can cause startup issues and other errors. If compatibility mode is enabled in Outlook, disable it. Follow these steps:

• Find Outlook.exe in the installation directory. The default path is: C:\Program Files\Microsoft Office\OfficeXX or C:\Program Files (x86)\Microsoft Office\OfficeXX.
• Right-click on Outlook.exe and select Properties.
• Go to the Compatibility tab and uncheck the Run this program in compatibility mode for option.
• Click Apply > OK.

Method 6: Exclude Outlook/OST from Antivirus Scanning

Antivirus programs can temporarily lock the OST file while scanning, preventing the Outlook application from accessing the data file and triggering the errors. You can check if your antivirus program is causing the problem by temporarily disabling it. Follow these steps:

Note: Disabling antivirus protection may expose your system to security risks. You can re-enable it as soon as you complete the test.

• Open Windows Security and go to Virus & threat protection.
• Click Manage settings and temporarily disable real-time protection.
• Restart Outlook.

If your email client opens normally, it means your antivirus software is causing the issue. In that case, you can exclude the OST file and Outlook from your antivirus software’s exclusion list. Here’s how to do so:     

• Find your OST file path by pressing Windows Key + R and typing LOCALAPPDATA%\Microsoft\Outlook\.
• Note the exact folder path or the .ost file extension.
• Open the Windows Security app and click on Virus & threat protection.
• Click Manage settings, under Virus & Threat protection settings.
• Scroll down and click Add or remove exclusions.
• Click Add an exclusion and choose the .ost file or folder path.

Now, restart your computer and launch Outlook again.

Method 7: Create a New Profile

If your Outlook profile is corrupted or damaged, it may fail to open the OST file, resulting in errors. To resolve this, you can create a new profile and remove the corrupted one. Here’s how:

• Close Outlook and open Control Panel.
• Navigate to User Accounts > Mail.
• Click on the Show Profiles button. Then, click Add.

• Type any name for the new profile and click OK.

• You will see a sign in wizard. Enter your email account credentials, such as username (email) and password to log in.
• Once the sign-in is successful, restart Outlook.

If it works without any issue, you can remove the old corrupted profile.

Method 8: Run the Inbox Repair Tool

One of the major reasons for the “OST file cannot be opened” error is corruption in the data file. Microsoft provides ScanPST or Inbox Repair tool to repair corrupt Outlook data files. You can repair your OST file using this tool to resolve the issue. Here’s how:

• Locate ScanPST.exe (The location depends on your Outlook version).
• Close Outlook completely and launch ScanPST.exe.
• Select your OST and click Start.
• Wait for the scan to complete. If errors are detected, click Repair.

Once the repair process is finished, restart Outlook.

Method 9: Recreate the OST File

If none of the above methods works, you can recreate the OST file. For this, close Outlook and go to the folder where the OST is located. Take its backup by moving it to another location or renaming it with the .bak extension. When you start the application, it will automatically recreate the OST file at the default location on your system and synchronize the mailbox items from the server. Depending on the mailbox size and internet speed, the synchronization may take some time.

If your Account is Disabled or the Domain Changed?

If your Outlook account has been disabled or the domain has changed, then the OST file linked to that account becomes orphaned or inaccessible. You cannot even open or import this file into another profile.

In such a case, the only option is to restore mailbox data from the file by using an advanced converter tool of Stellar Converter for OST. This tool is designed for converting inaccessible and orphaned OST files to PST format, which can be easily imported into any Outlook profile. It can convert all the file items, including emails, attachments, calendars, contacts, and notes with complete precision. It also supports exporting the OST file data to Microsoft 365 (Office 365). The tool supports Outlook 2024, 2021, 2019, 2016, 2013, and earlier versions.

Watch this video to know how this tool works:

Conclusion

The Outlook OST file cannot be opened error may occur due to faulty add-ins, damaged/corrupt OST file, and various other reasons. However, you can easily resolve the error by following the solutions mentioned in this blog or use an advanced OST to PST converter tool of Stellar to extract data from such an OST file. The tool converts the file into Outlook PST format which can be easily imported into any Outlook account.

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