Error: java.lang.RuntimeException: Widget disposed too early
I followed many solutions on IBM's pages and tried different versions of my software (it said that it was a Firefox fault), but nothing helped me. Finally I tried with overriding the .metadata folder from my old RAD's workspace and it actually worked!
I found also on the Developer Works forum (http://www.ibm.com/developerworks/forums/thread.jspa?messageID=14385876) that some other people tried the same as well and it also worked for them.
At the end I have to say that under Linux RAD works twice as fast (but not as fast as it should and could) so I can highly recommend Linux as the platform for these havy-waight Eclipse tools.