Getting outlook.ost is in use when opening Outlook after booting up.

We have a customer who when they start up their PCs. They get an error message saying the outlook.ost file is in use. ( see screen shot attached). It is happening on all users.
Sometimes it will take one attempt to open outlook. But other times it will take 10 attempts of clicking ok on the error before being able to open outlook.
They are all Windows 7 x64 PCs running Office 2007 with Business contact manager, so they all have to run in cached mode.
The server is an SBS 2003 server running exchange 2003.
I have tried everthing i can think of to try and resolve this issue but whatever i try doesn't seem to work and they keep getting the error message up.
At first we thought it was symantec as it seemed to fix the issue when ending the Protectionutilsurrogate.exe process. But i completely uninstalled symantec and the error still kept happening.
I have also uninstalled the windows search feature from Windows 7 and also completely recreated the outlook profile but this hasn't fixed the issue.

Has anyone ever come accross this issue.

Any help would be greatly appreciated.
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First thing I'd do would be trying to use Unlocker to unlock the file.
You can log in as admin and rename the .ost to .old and then restart, when the client logs in it will create a new .ost.
It is safe to delete the ost file. The ost file is an offline cache of the exchange server. You can also go into control panel email settings,  email accounts advanced settings and uncheck teh box for caching. Then restart Outlook and re-enable it. The file will be rebuilt.
brasso_42Author Commented:
I have taken outlook out of cached exchange mode. And it now opens up first time every time.
But i'm now having an issue where any emails go into the outbox first before being sent.
I have to close out of outlook and reopen it and then do a send all to be able to get the messages to send.
Have you tried renaming the OST file and going back to cached mode?

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