I tried turning off the machine and letting it sit unplugged for a few hours. Then I started it with no cartridges in it, which is supposed to force it to reset all of its level indications. Before putting in the MIS cartridges, I refilled them. (They were nearly all empty and I had yet to print a single page!) I hit the ink button and the printer parked the head as it should. I loaded the six, full MIS cartridges. The printer went through its normal post cartridge change cycle and then went into the locked-up condition with both the ink and paper jam lights flashing together.
The problem persists.