> The docs say the rebuilder only produces valid files. But if I rebuild from my
> rom collection, and use the scanner on the rebuilt roms, errors still show up.


Well..because roms aren't sets. A set got several roms and the rebuilder only rebuilds valid roms. That doesn't necessary mean you got full sets of course. Read the documentation about the rebuilder and you'll know how it works.

Mainly to get a clean collection you do:

1) load a datfile in the profiler
2) setup rompaths in the scanner
3) scan with all check and fix options enabled

After that you should get a list with either no entries at all (-> you're done) or with missing files and maybe some badsized files or files with a bad checksum. You have to find the correct files for these and add them to your collection. Adding can be done with a) fix missing + addpaths in the scanner or b) with the rebuilder.

You may also check out some tutorials about ClrMamePro in the internet, e.g. at mameworld.net/easyemu

Roman Scherzer
ClrMamePro