When attempting to connect to a Server 2008 TS Web Access site, you may see the following error displayed:
I have read this is the expected behavior if your remote desktop connection is below version 6.1. RDC version 6.1 is included with Windows Server 2008, Windows Vista SP1, and Windows XP SP3.
The machine I was using was running Windows XP SP3 workstation however. To correct, I read some folks added the TS Web Access page to their Trusted Sites settings within IE. I tried that first but the problem was not resolved. To ultimately resolve this issue, the following steps were taken:
1. Within IE, click Tools | Manage Add-Ons | Enable or Disable Add-Ons
2. On the Manage Add-ons window, the Terminal Services ActiveX Control is likely disabled. With the Microsoft Terminal Services ActiveX Control highlighted, under the Settings heading, click Enable and OK.
3. Close and re-launch IE. Navigate to the TS Web Access page and login to see your RemoteApp Applications