yeah, theres a number of things that can cause mmenu to blow up during the skin process; it was supposed to have an auto-backout solution (if it tries to load a few times in a row, in very quick succession, assume a crash and go back to no-skin mode), but I forget if that ever got checked in. I coded it, but I think it fell through the cracks.
Its been too long, I forget now.. missing artwork was supposed to fall back to default known-artwork and such, but certainly, so outright bad configs could cause crashes. I used to run mmenu by hand (from xfce and shell say), to witness the log of issues before it blew up. But just changing a skin, and rebooting the pandora, is a sure way to frustration.. need to (ironically?) fire up mmenu from non-mmenu in the skin development process.
Ultimately, skinning wasn't too flexible -- it was mostly to let you sub in different artwork and tweak positions a little; it was never super flexible (all the oddities fall out of the afact, that mmenu was born due to Craig asking 'hey, can you make a new menu since the other one isn't coming together in time, and we need it in a week'.. so mmenu was written I think in 3 days after work. That shows, a lot
jeff