When Remote Desktop Service try to connect ,

Error.
All desktop sources available on this desktop are currently busy.

is displayed, the number of concurrent users on the Remote Desktop Service server (approximately 30 or so) has been exceeded.
Try again after a while.

For faculty members
– Assignments using a remote desktop service for online classes –
The Remote Desktop Service is intended for temporary use at home and other locations.
The number of users that can be connected at the same time is limited to about 30.
Please instruct students to move the time of use to a different time of day or minimize the time of use.