Here is how to produce this problem.
1. Open two files. I opened one visual (form based) class and one Java Bean class.
2. Switch to the other file using the drop down in the upper right hand corner of the IDE.
The cursor in the editor goes away and you can not type any more. I can highlight but I can not edit.
Mac OS X 10.4.2
java version "1.4.2_07"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_07-215)
Java HotSpot(TM) Client VM (build 1.4.2-50, mixed mode)
*** This issue has been marked as a duplicate of 60235 ***