Sure. Take the
String class. Say that it contained a member variable in java 1.2, which was subsequently removed in version 1.3. Now, if you serialize across 1.2 VM to another 1.2 VM, then there's no problem, because they both expect that variable to be there. However, from a 1.2 to a 1.3 VM, you have a problem, because you're trying to fit this variable into a new, 1.3 class that isn't prepared to recieve it.
However, in reading over the original question again, I wonder if I'm answer a question that wasn't asked. That is, I'm assuming that when you say different VM, you mean differnt versions of the VM. IF you mean the same version, then there's no problem.
HTH,
M, author
The Sun Certified Java Developer Exam with J2SE 1.4