The Task You Are Trying To Do Can't Be Completed – Citrix

When trying to log into a Citrix connection, I get:

The task you are trying to do can’t be completed because Remote Desktop Services is currently busy. Please try again in a few minutes. Other users should still be able to log on.

Unfortunately the Citrix server with the issue is hosted by a third party, so I can’t see if it’s under too much load.

To fix this, I waited a while (the error went away after 5 minutes, but I still couldn’t log in), then rebooted the computer – after which I was able to log in without the Remote Desktop Services is currently busy error.