Or maybe he just had a couple boards and sent the wrong one? Oh wait, everyone selling Amiga stuff is a crook these days, lol. :p
Not sure off-hand where the MMR maps its memory, but if you already have 8+2MB you may be about hitting your limit.
FWIW here's how I did my A500:
8MB 32-bit RAM on the VXL*30 (doesn't autoconfig, requires a separate tool in the S-S to add it then reboots)
8MB 16-bit RAM in the GVP sidecar
2MB chip (512k on motherboard, 512k in the trapdoor slot, 1MB on a MegaChip)
I just like being able to say my A500 has as much memory as an A3000 back in the day, and with a mild 30MHz overclock is faster, too. Lol.

Edit - sure would like to get my hands on one hand those 128MB Derringer's, someday!
