The ability to target the common language runtime from several languages means that clashes are possible when a word that is reserved in one language is used as the name of a namespace, type or member in another.
It seems that not all C#/VB/{cpp} keywords are reported by this rule and there is no list of the keywords FxCop matches.
We are postponing the development of this rule because of its small target audience (it is best suited for library developers, who's products will be used in different languages).