I spoke to Animas Tech Support. This is what they said.
They acknowledged that as this stops insulin delivery it should be classed as Alarm not Warning. Or at least it should be recorded in the pump History (it isn't; Warnings aren't).
It can be caused by a bad cartridge that doesn't move smoothly. (If the pump also asks for a rewind, then it's a power failure of some kind.)
Once a week or less they say is acceptable. Three times a day for the last 2 days (and 2 new cartridges) is not acceptable, they say.
The initial response is to change the insulin reservoir cartridge.
Physically what's happening to the pump? What's it detecting?/It means an internal positioning sensor thinks the cartridge has moved away from contact with the piston rod. Can be a sensor error, bad cartridge, mechanical shock moving the cartridge.