MAMEWAH v0.90 will not work with MAME32.
For Windows MAME, MAMEWAH will read you ROM path from MAME.INI (or MAMEPP.INI or whatever),
For DOS MAME, MAMEWAH will read your ROM path from MAME.CFG.
I would suggest either install v0.95b and overwrite with the v0.952b update, or wait a day or so for v0.953b

BTW I would still not suggest using MAME32, so it might be worth your while trying Windows Commandline MAME...