Terminal Server Easy Print is not supported if the RDC ActiveX control is being run in WOW64. This will usually occur if you are running a 32-bit application that calls Mstscax.dll, and the operating system is 64-bit. This will cause the control to run under a virtualized 32-bit environment (WOW64).
In this configuration, Terminal Services Easy Print will not function.
Using Terminal Services Easy Print Driverhttp://technet.microsoft.com/en-us/library/ff519199(WS.10).aspx
for other considerations.