File access is denied .ost

Hi guys,

I have users with an additional mailbox attached to their profile.
When they try to access the mailbox by starting Outlook and choosing the necessary profile they are presented with the following error:

File access is denied. You do not have permission required to access the file C:\PROGRA~2\Office14\email@address.com – name.ost.

These guys are local admin on their respective machines.
Are there any Outlook settings which could cause this? 

Environment:
Exchange 2010 SP1
Clients use Outlook 2010 x86
Client OS – Windows 7 x64

Please let me know if there is any other information required.
Any help would be greatly appreciated.

Regards,
Locust12