Problem with OCS and Windows 7 machines

Hello there,
We have a server running OCS 2007 R2. It has been working fine for a number of weeks but last friday we had to rebooted and since them all clients that are running Windows 7 are getting a red exclamation client on the OCS icon and the following error " Cannot synchronize with the corporate address book. This might be because the proxy server setting in your web browser does not allow access to the address book.
If the problem persist, contact your system administrator". Windows XP clients are not affected.
