1. Start>Run> regedit
2. In the regedit console, browse for or navigate to the key HKLM\SOFTWARE\Microsoft\MSLicensing
4. Right click on the key name “MSLicensing” and select DELETE.
5. Close Regedit
6. Do NOT open any shortcuts for Remote Connections at this point. Instead, you need to open the Remote Desktop Connection Manager. It’s VERY important that you do this by RIGHT clicking on the program and selecting “Run as administrator”. If you don’t do this properly, the registry key you deleted in step 4 will not be recreated. The Remote Desktop Connection Manager can be found at: START>All Programs>Accessories>Remote Desktop Connection.
7. Select the remote connection you want to use and click “Connect.” If you have done this properly, a new registry key will be added that will have updated licensing information.
MS reference :http://technet.microsoft.com/en-us/library/cc756826(v=ws.10).aspx