I’ve got 2 exchange 2003 servers in different domains. It seems on about a monthly basis that the ActiveSync just stops working and my mobile users get shut off from syncing.
Today I found a quick little workaround.
Over in EMS, right click the HTTP virtual server container and uncheck forms based authentication. Restart IIS. Go back and check forms based authentication back on. Restart IIS.
Simple, but saves me a lot of headaches trying to narrow down the issue.