For those still using RDS on Windows Server 2008 R2; a new KB was released (3014783) that fixes the “The task you are trying to do can't be completed because Remote Desktop Service is currently busy” issue. (Need help moving to 2012R2? let me know! :)
“…This article describes a problem that occurs when you log on to a computer in Windows 7 Service Pack 1 (SP1) or Windows Server 2008 R2 SP1. A hotfix is available to resolve this problem. The hotfix has a prerequisite.
When you log on to a Windows 2008 R2-based server and access an application by using Remote Desktop Protocol (RDP), you receive one of the following error messages:
The task you are trying to do can't be completed because Remote Desktop Service is currently busy.
The Group Policy Client failed the logon.
This problem occurs because of a synchronization issue in the user profile service (profsvc) between the work thread and the main service routine. When the user profile service stops, the service might still be busy trying to clean up the profiles…”