How to Fix File Username .ost is in Use & Cannot be Accessed Error?

OST file is of great use in MS Outlook but, you may face several issues while working with OST in MS Outlook. Every time you encounter any OST file error message, the most workable solution is to convert OST to PST. This method helps you to migrate complete data from an erroneous OST file into PST file format and you can easily open it in MS Outlook.

Same is the case with “file username .ost is in use and cannot be accessed” error. These messages do not just hamper the work, but they may also lead to permanent data loss if not corrected properly. You might encounter this error message while trying to open the OST file. It severely restricts opening your OST file. Also, you might get to see a yellow triangular warning sign on Outlook account. To resolve this error, you first need to understand the cause of the error.

Some of the possible reasons for getting the above-mentioned error are as follows:

  1. Synchronization issue between OST and MS Exchange Server.
  2. Conflict of some other programs with MS Outlook.
  3. Unauthorized access of the OST file.
  4. When any other process that uses .ost file is running in the background like Communicator, Lync, Ucmapi, etc.
  5. Multiple users are working on one OST file at the same time. 
  6. Internet connectivity issues could also be the reason. 

Thus, any one of the possible reasons listed above or any other hardware issues may lead to the error, “file username .ost being in use and cannot be accessed”. Now that you know the possible causes instead of panicking, find out the solutions to overcome this error.

List of different techniques to solve this error:

Method 1 – Close the MS Outlook application. Look for other related applications running in the background, and; close them too. Follow the below-given steps:

  1. Close MS Outlook application
  2. Right-click on the taskbar and choose the Task Manager option 
  3. Select the first tab called “Processes”.
  4. Now, look for the applications named Microsoft Outlook, LYNC, Communicator, or UCMAPI.EXE. Select them one by one and close each task by clicking the “End Task” button
  5. Now restart your computer and try to open Outlook again 

Method 2 – Disable Cached Exchange Mode to fix the issue.

  1. Close Outlook and Open “Control Panel” 
  2. Choose Mail option 
  3. Then select the Email tab in the Email account option
  4. Choose the email address showing the error and then select “Change“.
  5. Now Uncheck “Use Cached Exchanged Mode” option
  6. At last, select “Next” then click on “Finish “ 

Method 3– Try to remove defective Ads-ins, sometimes removing defective Ads-ins will help you to solve this error

  1. Open MS Outlook select file and now click on the Ads-in option
  2. Now, select the Ads-ins option in the Manage header the click on Go
  3. Now click on OK

Method 4– Run scanOST.exe utility, which is an inbuilt tool of MS Outlook used to scan corrupt OST files. This tool works for synchronization issues but fails to repair damaged and corrupted files. It will work until the 2007 version only.

If neither of the above-given techniques works and; you are still unable to fix the error, then I would suggest going for an OST to PST converter. It will convert your corrupt OST file to PST and make your OST file accessible again. This option is also feasible if the OST file is an orphan file, and you cannot open it due to the lack of appropriate software in your machine.

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