Disable Cached Exchange Mode
- Close Outlook.
- Select the Windows Start icon > Control Panel.
- Select Mail.
- Select Email Accounts.
- Select the Email tab.
- Highlight the email address giving you the warning (email.ost), then select Change.
- Either tick or remove the tick from Use Cached Exchanged Mode.
- Select Next.
- Select Finish.
End 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.