I know that it won't help you but I've run tests (using Screenscraper as server source, TheGamesDB is not the best source for Mame!) and everything is working nicely (thousands of snaps, logos and movies downloaded successfully)
How many games do you see listed for MAME in the "DB Edit" tab of mGalaxy? Can you see that they do have a proper "description" name (that the 'real name' is displayed) ?