Sometimes, and it seems to happen predominantly with the new gray receivers for the CPS Clicker system, a class will try to enter an answer into their clicker, and it won't get sent.
The problem? The receiver's cache is full. You have to go to the eInstruction device manager, select the receiver and then go to help --> clear device properties, then click ok in the next window that pops up. You can do this while a test is going on.
You might also need to turn off and then back on the clickers that are affected.
There is an update to the software that should get rid of the problem, but it breaks other things about CPS so we are avoiding the update for now.