While using Microsoft Outlook, it is quite possible that you might get stuck with an issue. Though each error may relate to a specific part or functionality of Outlook, for the first time, it’s hard to know the reason that why exactly it happened.


  • Execute All Outlook Processes
  • Restart your PC
  • Disable Cached Exchange Mode
  • Use a Professional Tool
  • Conclusion

Outlook Data File – The file C:\Users\user name\AppData\Local\Microsoft\user name\username.ost is in use and cannot be accessed. Close any application that is using this file, and then try again. You might need to restart your computer, is one out of many errors which possibly can occur on your system. Many Microsoft Outlook users search on the Internet to find a resolution over the same.

In this article, we’ll go through a couple of workarounds which can help you come over the error and resume your work again.

End All Outlook Processes

End All Outlook Processes

Check for all current Outlook processes running in the background. Kill all the processes which relate to Outlook.

Follow the steps below:

  1. Right-click on the taskbar > select Task Manager.
  2. or
    Press CTRL + ALT + Delete > select Task Manager.

  3. Move on to the Processes tab.
  4. 3. Here, look for processes with name Communicator, Lync, ucmapi or Outlook. Kill all the processes related to these.
    (Select the Process > click End Task button).

Restart your PC

Restart your PC

You can continue trying to end all the Outlook processes, but it might take all day, and you may end up by getting nothing, maybe.

Instead of looking for the process which might be disturbing the Outlook OST file, you can try restarting the system.

  1. Hit Windows to pop out Start > Select Restart.

Disable Cached Exchange Mode

Disable Cached Exchange Mode

By disabling Cached Exchange Mode, you can try to fix the issue because Outlook no longer will be syncing your mailbox data with the OST file on your system, which may affect the accessing speed, as you would be accessing your mailbox directly from the Server.

Follow steps below to Disable Cached Exchange Mode:

  1. Close Outlook.
  2. Launch Control Panel > select Mail.
  3. Click Email Accounts button.
  4. Move on to the Email tab.
  5. Select the Outlook account (mail address) giving the error > select Change.
  6. Uncheck Use Cached Exchanged Mode.
  7. Hit Next > click Finish.

Use a Professional Tool

When none of the manual method works and there remains nothing which you can do by yourself to get rid of the issue, then using a professional tool would be the best option available.

Using an OST to PST converter tool, you can convert the Outlook data file type (format) and convert the Outlook OST file to Outlook PST file, which automatically will eliminate the file cannot be accessed problem.

OST to PST conversion

After the OST to PST Conversion, you can import the PST data file using Outlook’s built-in Import/Export utility.


Outlook errors suddenly popping on the screen is very uncommon, but it is not certain either that you may not face one. Professional OST2PST converter tool to cover such situations.