Drive Mappings are assign in the vWorkspace Management Console. These do not appear when a User logs into a 2008r2 Terminal Server.
Turning on PNShell logging reveals Error 1326 adding drive mapping
Local Security Policy prevents sending credentials in a format that older OS's understand.
1. Click Start | Control Panel | System & Maintenance | Administrative Tools
2. Double Click Local Security Policy
3. On the left pane, click to expand Local Policies
4. On the left pane, click on Security Options
5. Now, on the right pane, near the bottom, click on
Network Security LAN Manager Authentication Level
6. On the drop down, change the default setting (NTLMv2 only) to
"Send LM & NTLM - use NTLMv2 session if negotiated."