Langleyben Leon has some gripes with Team System Work Item Field Names.
Work item name can not contain underscore or other not alpha-numeric characters. Spaces are allowed. Just spent some nice time replacing underscores in Work Item type fields migrated from ClearQuest. CQConverter migration tool did not consider it a problem.
This is an issue in Beta 2, but we've addressed this since the Beta 2 builds. In beta 2 there is a restriction that "friendly" names for fields could only contain a very narrow set of characterstics. This was because of a coupling between the field names and column names we used in the database.
However, post Beta 2, we changed this and we'll allow any characters for the field friendly names. For the formal reference names you will be able to use alphanumeric characters, periods, and underscores. Hopefully this will solve his problems going forwards.