Office Communicator and cannot sync Address book error

We are trying to get OCS 2007 R2 up and running. The clients login fine, but when I let it sit for a while, we still get the address book sync error message of:

"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".

When I try and download the file locally, this error comes up:

Could not load file or assembly 'ABServerHttpHandler, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. Failed to grant minimum permission requests. (Exception from HRESULT: 0x80131417)

I googled and came across this post (http://social.technet.microsoft.com/Forums/en/ocsaddressbook/thread/c28ff2d8-66a4-456c-a5ad-e445a667e8ed) which suggests removing and reinstalling .NET 2.0 but that didn't seem to resolve the issue either. When we run abserver.exe -validateDB it works properly.

We even tried the suggestion from Greg's Blog (http://blogs.technet.com/greganth/archive/2009/03/11/office-communicator-notifications-cannot-synchronize-address-book.aspx) about restarting the web component services but that didn't work either. Still seeing the same issue. So does anyone have an idea of where we go from here?

Turns out it was an IIS trust issue. When I set the site OCS was setup on to Full Trust, it started to work properly.