Mike,
Though I don't know for sure because I didn't develop LabVIEW, it only makes sense to me that VI Server can only work with the version of LabVIEW VIs for which it was written. I recommend upgrading your older machine, or at least, recompiling all of your VIs in the newer version of LabVIEW.
Basically, to answer your question: Yes, there is a compatability issue between the two versions. I'm not sure what you are trying to do. If you could provide a more detailed explanation, perhaps someone can stir you in the right direction to solve your problem.