Dowland,
Thank you very much for summarizing the issue so well. I have read through pages and pages of posts to try and fix my "invalid PID checksum" problem with my copy of mobidedrm005. Even the 1st 6 pages of this thread....shows I should read backwards on threads here

)
Being of suspicious mind I now wonder if the repeat code has been deliberately added to discourage people from trying to strip the DRM off mobi files.......I might hurriedly add that I actually got the faulty mobidedrm005 script from another site!