If At Ease is turned off through the At Ease Administrator, taking screen shots are disabled on all At Ease workstations, even if screen shots were not previously disabled when At Ease was on.
Workaround
If you need to have At Ease off and have the ability to take screen shots, you will need to either disable, or remove the At Ease Startup extension on the workstation.
Apple engineering is aware of this, however, there is no known time frame for a fix being made available.