Going by this thread at The Session, the mandolintab converter has been broken for a few weeks. A few people have tried to contact the site owner, Simon Becker, but have had no reply.

I think Helen is wrong in her suggestion so here’s mine…

When I had the converter at folkinfo, I wanted the option to run the conversion routines which run a few executables (abcm2ps, ghostscript, etc.) on a different server to the web server and the converter is in 2 parts – a backend and a frontend. The frontend on the version of the converter passed on to Simon sent an “access code” to the backend as part of its data. I can’t find the backend code for that version to be certain but I think the backend terminating and returning “unauthorised” is what happens when the access code sent by the frontend doesn’t match the backend.

If I’m right, I think the problem would be easy to fix IF Simon could be contacted.