Description of problem: /usr/bin/mdtool is a wrapper around a Mono executable. Sadly, the path is wrong on 64bit. It contains the line: EXE_PATH="$PREFIX/lib/monodevelop/bin/mdrun.exe" However, mdrun.exe is under $PREFIX/lib64/monodevelop/bin here. I'm not sure what's wrong here: clearly the path needs to match reality, but I'm not convinced that the executable is actually 64-bit rather than 32-bit. I would have thought it was arch-neutral personally. One or the other needs to be fixed, though, cos otherwise I can't execute mdtool :) Thanks.