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Know-How to Solve the Error: "The file username.ost is in use and cannot be accessed" Safely

Did you know if a user is using Exchange Server with Cached Mode on, then a duplicate of the mailbox is created on the system? This duplicate file is stored within an OST (Offline Storage Table) file. A user can continue to operate the OST files even when there is no internet connection. All the changes made in the mailbox are consolidated when there is internet connectivity. However, there are disadvantages as well as OST files can get corrupt or the user faces an issue while moving the data to another system. Often, the user faces many errors while using Outlook and if a pop-message, "The file username.ost is in use and cannot be accessed" displays on the screen, then don't worry as this blog entails the detail on how to fix the error and what are the reasons behind the error.

Reasons behind the Outlook Error

While using the 'Save and Send' option in Microsoft Word and PowerPoint, most of the users have already experienced an error, "the file xxxx.ost is in use and cannot be accessed". This error implies that the Outlook file is used by another program or the reason behind the error could be several:

  • Synchronizing process of an OST file and Exchange Server mailbox
  • When several users are trying to operate the same OST file
  • Unstable internet connection
  • Some Processes such as UCMAPI.EXE, LYNC, and etc. running in the background is another reason behind the error
  • Faulty add-ins in Outlook

Know Different Ways to Solve the Error: "The file username.ost is in use and cannot be accessed"

The user can opt for any one of the below-mentioned methods to solve the error, 'The file username.ost is in use and cannot be accessed'.

  • Shutdown Microsoft Outlook and Other Processes
  • One of the common reasons behind the error is when the user runs Outlook and other processes. It can corrupt the OST file and cause the error so ensure that you exit MS Outlook and other processes. Let us have a glance at the steps:

    • Exit Outlook on the system.
    • Now, open the 'Task Manager' option.
    • Click on the 'Processes' option.
    • From the available options, select UCMAPI, Outlook, Communicator, and LYNC.
    • Now, click on the 'End Task' tab.
  • Disable the Cached Exchange Mode
    • Open the 'Control Panel' option.
    • Click on the 'Email Accounts' tab.
    • Now, choose the email address and double click on 'Change'.
    • Then, uncheck the "Use Cached Exchange Mode" option.
    • Click on the 'Next' option.
    • Click on 'Finish'.
  • Disable Outlook Add-ins
  • As a matter of fact, add-ins enhance Outlook's functioning, however, faulty add-ins can create errors and hamper the working of Outlook. We recommend you to disable add-ins and you can do it by starting Outlook in 'Safe Mode' and type 'Outlook in the Run Dialog Box'. Let us find out, how a user can launch MS Outlook in Safe Mode:

    • Locate the shortcut icon for MS Outlook.
    • Now, hold the 'CTRL' key.
    • Click on the shortcut icon for MS Outlook.
    • Click on 'Yes'.
  • Repair Outlook OST Files Via'ScanOST.exe'
  • Microsoft Outlook has an inbuilt tool, 'ScanOST.exe' that allows the user to resolve the minor errors. The user can resolve the error, "The file username.ost is in use and cannot be accessed" by using 'ScanOST.exe'. But, sadly this tool is available only in Outlook 2010 and lower versions. Below are the steps to repair Outlook files via 'ScanOST.exe' method:

    • Open Outlook on the operating system.
    • Browse to the file 'ScanOST.exe' and click on it to start it.
    • Select the OST files that you wish to repair.
    • Locate the location of the OST file by typing "%LOCALAPPDATA%\Microsoft\Outlook\" in the 'Run Dialog Box'.
    • Rename the file.
    • Click on 'Repair Error'.
    • Click on 'Start Scan'.
    • Click on 'OK'.
  • Manual Method
    • Open Outlook and go to File > Open > Import.
    • Click on the 'Import and Export Wizard' tab.
    • Click on the 'Import from another file'.
    • Click on 'Next'.
    • Select the files that you wish to import.
    • Choose the location to save the file.
    • Click on 'Finish'.

The above-mentioned methods will not cost you a penny; however, all the methods have their own limitations and are unsuccessful in resolving severe damage. Using any of the above methods does not ensure 100 % positive result and consumes several hours to complete the procedure. Another disadvantage of using the manual method is that the user can execute the repair process only on Outlook 2010 and below versions. We recommend converting OST files to PST format in order to rectify the error by using automated software.

Solve the Error: "The file username.ost is in use and cannot be accessed" Via KDETools OST to PST Converter

To fix the error, the user can convert OST files to Outlook PST format by using KDETools OST to PST converter. The tool is well-equipped with advanced algorithms that allow the user to resolve any major or minor Outlook error without losing the data. It is the right pick for you if you are looking for a safe yet reliable way to resolve the error. The third-party converter ensures a positive result to the user. It is always recommended to opt for automated software over the manual method to solve Outlook error. The user can easily fix the error, "the file xxxx.ost is in use and cannot be accessed" if they use KDETools OST to PST Converter.


Fixing the error, "The file username.ost is in use and cannot be accessed" can be a tough task; however, if the user opts for an automated tool such as KDETools OST to PST Converter, then they can fix the error in just a few minutes without risking the loss of data. If you have failed to rectify the error by using the manual method, then don't give a double thought and use automated software to fix the error.

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