I've been seeing this more and more lately at work for some reason. The fix is super simple, it's just annoying as we have to have administrative privelages to access this file on our file servers at the restaurants in order to access these files.

In short, you just need to navigate to:
C:\Documents and Settings\<profile folder>\Local Data\Application Data\Microsoft\Outlook
You should see at least one *.ost file located in here. Rather than just delete the file, I would suggest renaming the extension to something else so that if something goes wrong for some reason, you do have the ability to go back and revert this file.