Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

You said "the old server 2003 it is already operating at the highest possible functional level: Windows server 2003"; but have you checked if this is actually true for both the domain and the forest? They can have different settings (i.e. a 2003-level domain in a 2000-level forest). You can check both levels in the AD Domains & Trusts console (pictures ...

Only top voted, non community-wiki answers of a minimum length are eligible