I don't know why it's happening. It happened to another guy who posted on the MAMEUI forum too. mameinfo.dat works OK. I narrowed the problem down to those dashes by deleting half of the file at a time until it worked. I wonder if it has to do with a font or language issue. What languages are installed on your PC? More than English?
EDIT:
OK, I renamed the roms folder and mameinfo.dat so MAMEUI wouldn't find them. I reopened MAMEUI and did an audit. It seems like everything shows up from history.dat. I renamed the roms folder and mameinfo.dat back and did another audit. It now seems to be working. Maybe not after a reboot though? Weird stuff.