Weird incompatible types problem...

I have a module A which depends on Hibernate 3.0.5
I have a module B which depends on Hibernate 3.0.5
B is a utility library, which is built, jarred and the jar file is in the libraries of A.

A uses B to create a hibernate Configuration file.

For some strange reason:
when, in A, I try to call the static method from B,

ibernateConfigurationFactory.createDefaultConfiguration();
it says: incompatible type, ... Configuration ... Configuration (which are of the exact same type).
If I remove the variable, select the method call and , the error reappears.

Where could this problem come from?

The weirdest is :
if I try to create 2 separate modules to reproduce the problem, to allow Jetbrains to fix it, it just disappears!: I create my 2 modules, adding Hibernate in the module libraries and Poof! the error is gone!!

How odd...