I upgraded my Quicktime and iTunes today and found that all of a sudden I couldn't compile anything in Eclipse! Apparently, the update got rid of the /System/Library/Java/Extensions/QTJSupport.jar file, and that shows up as part of the default Java 1.5 JRE definition in Eclipse. When it went missing, Eclipse freaked out.
The fix, found at note19 turned out to be simple.
Open the eclipse Preferences... menu and select Java > Installed JREs...; make sure that eclipse can locate the OS X Java 1.5. If it cannot (as was in my case), you manually add it. It is in the following folder:
Works like a charm now.