I have two projects/workspaces in Eclipse.

With the first one, I have created my project with Java 1.4.2 and this compiles fine. I must confess though that I made the project first with jdk 5.0 but eventually I switched to 1.4.2 and compile withouth any errors.

However, my new project with 1.4.2 I get exception:
Exception in thread "main" java.lang.UnsupportedClassVersionError
which means I should use jdk 5.0

I use the same hibernate.jar files for both.
Can anyone understand why this is? I have to use 1.4.2 unfortunatly, and the only solution seems to be to compile hibernate3.jar with 1.4.2