Very odd issues (often Mono not working at all) is often an either 2nd Mono install in PATH or a overwritten Mono install in /usr caused by a custom build from source with /usr as prefix instead of /usr/local or /opt.
Very odd issues (often Mono not working at all) is often an either 2nd Mono install in PATH or a overwritten Mono install in /usr caused by a custom build from source with /usr as prefix instead of /usr/local or /opt.