Distribution lists not updating when shared folders moved

I transitioned our Exchange structure from a 2000 SBS with Exchange 2000 to a
server 2003 with Exchange 2007. I have successfully moved the shared
folders.

In a shared contacts folder, there were several distribution lists. Each
had a mix of email addresses and contacts that was pulled from the shared
contacts folder.

Now when we try to use or update the distribution lists, it says it can't
find Contact xxxxxx. It has been moved or is no longer available. Do you
wish to delete xxxxxx?

The contacts are still in that shared contacts folder on the 2007 server, as
are the distribution lists. I'm convinced it is looking to our old Exchange
server for validation of the contacts. Is there a way to point the
distribution lists at the new server so it can find the contacts and validate
properly?