Looks like the guys on SlotTechForum have run across it. Appears to be a software bug. Here's what they say IGTs response was to the issue:
"I found the notes on the Assertion Failure … it is the complicated setup that exposed the issue. The bottom line to the attached notes is that if you bring the game up, close the door, and go into at least one tab menu and then keychip the machine, you will not see the issue. We have already fixed this in the upcoming Game King 6.3 release … due out next year.
Conditions for the problem to occur:
Games enabled for the first tab (usually the poker tab) must have no games enabled of another type (tab) that has a lower game index (like slot) on the lowest denom of that first tab.
Also, there has to be 13 or more games enabled on that first denom of the first tab.
Also, one or more games on the first tab must have a progressive enabled.
Example:
Clear RAM and E2.
Set the accounting denom to 1c. the machine will reboot.
Go into keychip without closing the door first.
Disable all slot games (use the family filter to show only slots and disable).
Enable Jacks or Better with one Stand Alone progressive level.
Exit the operators menu. (machine reboots here)
Press OK to verify options.
Close the door.
---> System Error.
Workaround:
To work around this problem requires that the machine be allowed to run the main menu code on the default game set with no progressives and you must touch another tab.
Do this before keychipping and setting up your game set and the progressives."
Hope this helps!