Microsoft Outlook 2016 crashed on me today. When I tried to launch it again, I received an error that said:
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.
Restarting my computer was not an option at the time. Here’s how you can solve the issue.
Fix 1 – Kill All Outlook Related Processes
- Right-click the task bar and select “Task Manager“, or press CTRL + ALT + Delete, then choose “Task Manager“.
- Select the “Processes” tab.
- Look for anything named “Communicator“, “Lync“, “ucmapi” or “Outlook“. If you find any items related to these, select it, then select the “End task” button.
Fix 2 – Restart Computer
Rather than spend all day trying to figure out the process that is hogging the file, try just doing a simple computer restart. Select “Start” > “Restart“.
Fix 3 – Disable Cached Exchange Mode
- Close Outlook.
- Open “Control Panel” and select “Mail“.
- Select the “Email Accounts” button.
- Choose the “Email” tab.
- Highlight the email address giving you the warning (email.ost), then select “Change“.
- Uncheck “Use Cached Exchanged Mode“.
- Select “Next” then “Finish“.
Now attempt to launch Outlook again. Hopefully, it works fine now. This is more of a workaround than a fix, as it switches to where you are using Outlook direct from the server. This may cause speed issues. If you have problems with Cached Exchanged Mode disabled, try enabling it again at a later time by rechecking the “Use Cached Exchanged Mode” box in step 6 above.
If neither of these fixes work, you might have another computer or program grabbing the OST file. Makes sure anything that uses Outlook is completely closed on any workstation that may interface with Outlook.
Thanks to Alix Jimenez for Fix 3.
Deven Malik says
You can also try out the steps mentioned below to resolve the issue
Appears that Cortana was holding onto the ost file too long.
Shedrach Oshofisan says
Thanks for this workaround fix. the third fix work for resolving the present issue.
Closing WebEx stopped this error appearing.
John Biard says
Like several others, method 3 worked for me. Thanks again
Closing Skype worked for me
Madhu Ammu says
Thank you very much…
Your recommended tip helped me to resolve the outlook issue that i have been facing for the last one month :-)
Narasimha Rao Taduri says
Thank you so much. You saved my time. Method 3 worked for me
M Ray says
Fix 3 worked great!! Thanks
Michael Wigle says
Fix number 3 fixed a problem where e-mail got stuck in the outbox and the progress details complained about not being able to access the outlook data file. Appreciate finding your post.
Bill K kapri says
Brah thank god youre a life saver
Edmund Esterbauer says
I removed the .ost account by deleting it and reinstalled the email account and it is now working. Thanks for the help of getting there.
Muhammad Asim says
Thanks Mitch, method 1 worked like charm. It seems one of the reasons why OST file gets engaged can be related to updates on machine and/or reboot. This is what i last did yesterday and today outlook would not start. Many Thanks!
Erwin Parker says
Closing Skype for Business before trying to open Outlook again does the job!