ServletExec to tomcat migration

[Mack dang]

Hi guys,
I have a very big Java/JSP project currently running very fine on ServletExec, but when I try to run the same JSPs on tomcat it is giving me errors. the errors are of type "cannot create bean of class", "Response already commited" and "illegalstate exception". All my class files are deployed in the classes folder in jar format and all the references are set for running my app., but still it is giving me the same thing. Can somebody tell me how to go abt. the migration.
Thanx & Rgds
Mack