Users are unable to reconnect to the original disconnected desktop session in Windows 2008.
Complete the following steps to resolve the error:
Open remote desktop session host configuration on the XenApp server in which the desktop is published.
Set the value of Restrict each user to a single session to No, as displayed in the following screen shot:
This error occurs because there is more than one server running XenApp with load-balanced published desktop. There are no other published applications.