Dear Benjamin, I see this issue on RC bug list, so I'm trying to help. (Though I don't have much knowledge on mono ...)
Seems FTBFS caused by lack of some mono libraries? So I guess there's something missing in Build-Depends in d/control? PS. This package has never been built on buildd. You should try source upload to prevent this. Thanks! Cheers, -- Roger Shimizu, GMT +9 Tokyo PGP/GPG: 4096R/6C6ACD6417B3ACB1