Upgrading from NT SP4 to SP6

I have a question about service packs. I have a client that has many domain controllers. All of them are at service pack 4. They have one server (member server), that is primarily used to host an ERP system (Jdedwards). They would like to upgrade just the service pack on that server, from service pack 4 to service pack 6a. Do you see any potential problems upgrading one server to service pack 6 and all other servers remaining at service pack 4?