How to Fix “The File username.ost is in use and cannot be accessed” error in Outlook?

When you receive the error “the file username.ost is in use and cannot be accessed,” it means that the OST file you’re trying to open is already in use by some other application. But, this is not the only reason behind this error, there are some other issues as well, such as;

  • Lack of synchronization between the OST file and Exchange mailbox
  • Weak internet connection
  • Unauthorized attempts to access the same OST file
  • Conflict of other programs with Outlook application

Methods to Fix This Error

There are several methods that can be used to solve this error. Some of them are manual methods that are not always helpful, and then there are third-party tools that can solve this error.

  1. Close MS Outlook and All Related Applications: One of the easiest methods to solve this error is the stopping and restarting of the MS Outlook application. Make sure that no Outlook application is running in the background as well. To end processes in the background, follow these steps;
  • Press “Alt+Ctrl+Delete,” and click on “Task Manager.”
  • A window will appear on your screen, now click on processes and look for “Outlook,” “Lync,” “Communicator,” or “UCMAPI” applications.
  • Select these processes one by one and press “End Task” to close these processes from the background.

Now, restart your computer and open Outlook, you might not face this error again.

  1. Disable Cached Exchange Mode: Cached Exchange Mode in Outlook allows users to work offline Exchange Server is not available. Disabling this feature can also solve this error. To disable this “Cached Exchange Mode,” follow these steps;
  • Close all MS Outlook application and open “Control Panel.”
  • Now click on “Mail” option in Control Panel, a window will appear on your screen.
  • Select “Email Accounts” from the opened window, and then choose “Email” tab.
  • Choose the email which is connected to Outlook, and then click on “Change.”
  • Now, disable the “Cached Exchange Mode,” and press “Next>>Finish.”

This technique can help you resolve the error.

  1. Kernel for OST to PST:

If you’re still facing the same error even after trying the above methods, then try a third-party tool to convert the OST file to PST. To convert the OST file to a PST file, you can use Kernel for OST to PST converter . The best features of this tool are:

  • Retrieval of deleted Exchange Mailboxes from damaged OST files
  • Recovery of complete OST data including deleted items
  • No file size limitations for the OST conversion
  • Preview of mailboxes before saving them
  • Convert OST file items to PST, DBX, MBOX, HTML, PDF formats

Now, let’s see how this tool works for fixing “The File username.ost is in use and cannot be accessed” error.

  • Download the tool from Kernel Data Recovery and Install on your system.
  • After launching the tool, a window will open on your screen asking you to select the file. Choose the desired OST file from the computer and click “Next.”
  • After the scanning process, all the items in the file will be visible in the left pane of the tool. Select a folder to see its items and click on a specific item to preview it.
  • You can save the file items in the desired format by selecting it from right pane of the tool. For e.g., choose “Save in PST” and click “Next.” You can also filter the file items based on their date, time, and item type before saving them.
  • Select the target where you want to save the file and click “Finish.”

After converting the OST file to PST format, you can easily access your mailbox items by opening this PST file in the MS Outlook.

Final Words: MS Outlook is a popular email client for Exchange Server and is widely used by small, large, and middle-level organizations for accessing user mailboxes. So, facing errors like “the file username.ost is in use and cannot be accessed,” can be tricky sometimes. But, with the help of above methods, such errors can be fixed.