If I remember correctly (and it's been a while, so forgive me if I'm inaccurate) if you change the rom location in Maximus Arcade it messes everything up. So you need to keep the folder structure intact when updating your roms. I believe it's case sensitive as well.
However, I haven't tried the new versions of MAME in ages. (I've stopped using Maximus Arcade).
Here's stuff to try:
Make sure you set the "Path to media" to "long" in the preferences.

Have you tried selecting: "(6) Option to choose whether MAME game descriptions are gathered from "mame.dat" file or from MAME XML generated game list."

Also, Maximus tends to generate it's own MAME.XML. Did you tried deleting it (make sure you back it up) so that Maximus will generate a fresh one?
Last but not least, the instructions say to edit the gamelist.xml, not the mame.xml:
"IMPORTANT NOTE: Newer versions of MAME (150 and above) require a modification to the 'gamelist.xml' file that is created by Maximus when you first run MAME. If you don't do this, you will get an "INDEX OUT OF RANGE" error. To fix this:
1.Open
gamelist.xml with Notepad. This file is big, so it will take a minute to open.
2.Hit Ctrl+H on your keyboard to open Replace.
3.Next to 'find what:' type "machine" without the quotes. Next to the 'Replace with:' type "game" without the quotes.
4.Click the 'Replace All' button, wait for it to finish.
5.Hit Ctrl+S to save your changes and then you can close Notepad."
Edit: Check out this topic.
http://forum.arcadecontrols.com/index.php/topic,145865.0.htmlD