I have not been able to find a post or get a true explanation on “reserved words” in BizTalk; however there are a few you should stay away from.  I have personally tested these.

You should refrain from using “BTS” or “EDI” anywhere in your namespace to avoid namespace property look-up issues.

I will be posting more about this as I work through the public version of BizTalk 2010 on Oct. 1, 2010.