Fix The file username.ost is in use and cannot be accessed

In our previous blogs we have discussed about the OST File format and how to open OST file. This article will be a quick fix to resolve Error “The file username.ost is in use and cannot be accessed” in Outlook. We can easily resolve this error with the CareUtils OST to PST Converter. Although there are some manual resolutions that you can try to resolve this error.  

This error mainly indicates that the Outlook.ost file that you are trying to open is accessed by some other program. We will first need to close that program so that Outlook can access that particular OST file. You may also require to restart your computer.

How to Resolve Error “The file username.ost is in use and cannot be accessed”

Resolution 1: Forcibly kill the applications using OST file. Just kill all the Outlook Related process running in background. To do this just open your Task Manager and then click on Process Tab. From Process Tab look for the item Outlook, Lync, Communicator or ucmapi. Select this process and then click on End Task button.

Resolution 2: If you don’t know which process is accessing the file and causing the error “The file username.ost is in use and cannot be accessed” then you can simply try to restart your computer. Most of the time you will be able to resolve the error with this easy fix.

Resolution 3: Try disabling the Cache Exchange Mode, as you disable the Cache Exchange Mode it will directly access the data from Exchange Server without involvement of OST file. If you need to use the OST file you can try enabling this option again.

If still you are facing the same issue while running Outlook application then there may be some other application that is holding the OST file. It can be some program or malware. In such cases you can use CareUtils OST Converter that will easily migrate the OST data to PST file format which you can easily import in Outlook email client.


In this short blog I tried to give you the best possible resolution for the error “The file xxx.ost is in use and cannot be accessed”. You can try this method in any version of Outlook including Outlook 2019, 2017. 2016, 2013, 2010 and other earlier versions of the Outlook. I hope you have successfully resolved this error with the steps mentioned above. If you are facing any difficulty while doing this process just leave a comment we would be happy to resolve your issue as early as possible.

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