Cannot synchronize with the corporate address book

Hi,

I have several users (including myself) that cannot sync with the corporate address book.  When opening OC R2 I get prompted for my domain password to access the address book.  It doesn matter if you put the password in or press cancel, it still logs in but has an exclaimation mark error over the address book (and on mine initially the exchange server).

The error is:

"Cannot synchronize with the corporate address book. This may be because the proxy server setting in your web browser does not allow access to the address book.If the problem persists, contact your system administrator"

I could contact him, but he is me! :)

Any help greatly appreciated.

Steve