Your MoMA definitions could be (much) older than the version of Mono you
are currently using. What version of Gendarme are you using ?
Gendarme 2.6 (preview) should try to download newer definitions (if used
with older MoMA definitions). Do a "man gendarme" and find where the
definitions are kept, then delete (or move) them. That should force the
rule to re-download the most recent definitions available.
Sebastien