mmm - wonder if I'm using the old or the new cfg format?
Open cfg/*.cfg file in hex editor
Look at the eighth character (first seven should be ASCII "MAMECFG")
If it's less than hex 09, the cfg is old.
History:
Mame used to have legacy code so it could read versions 08, 07, 06, 05 cfg files. AFAIK, 09 is the exact same as 08 except for having players 5-8 (version 0.74). 08 has been around since 36b16. Even cfg files 10 versions old often don't work or cause crashes, you better not be using the same cfgs since from .036b15!

clipk from (old) source:
/* header identifying the version of the game.cfg file */
/* mame 0.36b11 */
#define MAMECFGSTRING_V5 "MAMECFG\5"
#define MAMEDEFSTRING_V5 "MAMEDEF\4"
/* mame 0.36b12 with multi key/joy extension */
#define MAMECFGSTRING_V6 "MAMECFG\6"
#define MAMEDEFSTRING_V6 "MAMEDEF\5"
/* mame 0.36b13 with and/or/not combination */
#define MAMECFGSTRING_V7 "MAMECFG\7"
#define MAMEDEFSTRING_V7 "MAMEDEF\6"
/* mame 0.36b16 with key/joy merge */
#define MAMECFGSTRING_V8 "MAMECFG\x8"
#define MAMEDEFSTRING_V8 "MAMEDEF\7"