Typically this would be caused by the end user having multi-monitors: http://support.citrix.com/article/CTX125693/
In this scenario, changes were made to the server, either by a removal of the farm, or a misconfiguration which causes a registry key to be deleted.
Caution: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. Be sure to back up the registry before you edit it.
Complete the following steps to resolve the error:
- On the non working server open reg key: HKLMSoftwareWow6432NodeCitrixInstall.
- Look for a Binary entry called Setting. Note: If this entry is not present, shadowing will not work.
- On a working server, open reg key: HKLMSoftwareWow6432NodeCitrixInstall.
- Look for a Binary entry called Setting, you will see a binary number like the example below:
- Note the binary number on the working server and on the non-working server; create the binary entry called Setting at: HKLMSoftwareWow6432NodeCitrixInstall.
- Enter the number from the working server in the non working server.
You can read the entire article here.