Neither answer works. The location url appears to be http://marp.retrogrames.com/exe/(posted 9180 days ago).zip for all the betas available on the Versions page where = mameXX for full releases (XX version number) or = mXXbY for beta release Y of version XX. I have tried the obvious http://marp.retrogrames.com/exe/m36b1.zip
and more obtuse permutations with no success. Can you please be more specific, like actually specifying the url for Version 36, Beta 1 if it actually exists on this server.