Symptom
Other Classic applications do not open as expected after using a Classic application that calls on the Mac OS 9 Theater Mode extension. QuickTime Player 4.1.2 uses the Theater Mode extension.
Solution
Mac OS X 10.1 resolves this issue. Users of Mac OS X 10.0 to 10.0.4 can use the QuickTime 5 Player included with Mac OS X.
If the issue occurs with a different Classic application, disable the Theater Mode extension using the Extensions Manager control panel in Classic. You must then restart Classic.
Note: The Theater Mode extension is only present on computers that use it.