One of my co-workers, Peter Wong, came across this issue and struggled for quite some time to figure it out.

For some reason, running the product build on his development machine would pass all of the FxCop rules, but when other team members ran it, the FxCop spelling rules for identifiers would fail.

Turns out FxCop 1.35 uses the Office 2003 spell checker to do its work. The rules were failing on machines that have Office 2003 installed and passing on machines without Office because they weren’t actually running.  It only works with Office 2003 - you’ll see the same rules-not-running behavior if all you have is Office 2007.  Apparently, we’re not the only ones who have noticed this.  I sure never saw anything about it in the docs, but I guess I never really looked, either.

They’re working towards fixing this problem in newer versions of FxCop. Visual Studio 2008 code analysis tools have spelling rules built in and support custom dictionaries (won’t help folks without Team Foundation Server - it’s a policy you can configure). FxCop 1.36, which just came out in beta, ships the spell checker built in so you don’t need to have Office installed.