BizTalk 2006 :: Mapper :: XSLT

Hey everyone,

Is there something fundamentally different about the way BizTalk 2006
deals 
with a custom XSL file in a map than the 2004 version?

I have an XSLT which worked perfectly in 04 and now it fails.

I tried some other variations and I get errors such as "Data at the root 
level is invalid".

Can anyone help?

Thanks,
BA