If you're interested in what you did wrong:
When you see something like that, the game either has to update/ install itself to be playable. If you powered up a new machine it would do the same thing the 1st time. If you want to speed this process up you can either hold down "Insert" or hit F10 to turn off auto frame skip. (Hit F11 if you want to see the frameskip & speedup %).
What you did when you turned it off was interrupt this update process, so it thinks the power was abruptly shut off & you would have possibly messed up the pcb. MAME then saves this information when you exit the game as the nvram file you had to delete to reinitialize the machine. So when you restarted & got that error 81, that's the machine telling you that something messed up.
...from the source code:
Information from Guru
Seibu Kaihatsu SPI Hardware Overview
1995-1998 Seibu Kaihatsu Inc.
This system (known as 'SPI') consists of a main board and a plug-in
cartridge containing the game software. The games on SPI hardware can
be swapped by changing the top cartridge and then moving a jumper
to the alternative position. This re-flashes some ROMs for a few minutes
(accompanied by a techno music track). Afterwards, a message tells you to
put the jumper back to the original position and reboot the PCB. The new
game then plays.
TMI? Well now you know, whether you wanted to or not!
Pessimist: Oh, this can't get any worse!
Optimist: Yes, it can!