If you experience this problem from a Windows XP SP3 client, when you’re trying to connect to a computer on a SBS 2008 domain using Remote Web Workplace, you may experience this error.
A blogpost on technet blogs has this problem solved.
Follow these directions to get this problem fixed.
I still don’t know why this is becoming such a problem though, I’ve seen numerous problems with the Remote Web Workplace in SBS 2008 since I’ve started using it. First, the control was disabled, then SP3 disabled it again, and it’s now throwing this error.
One way around this would be to use a VPN, then RDP directly to the machine that you want to access. Of course, that would be completely bypassing the (supposed) ease of using RWW in the first place. If it keeps on being so difficult, I don’t see why using a VPN would be any harder to use though…