This is because of a bug/unsupported feature in dosbox's DPMI implementation.
[For the technically interested: DPMI function 0008 (Set Segment Limit) is called with an invalid segment value >0xffff, which is not allowed in 16bit mode. Afterwards, the CPU paging goes down the drain because of an invalid page link.]
If you try it with the "dpmi=false" config option, it tries to load its own DPMI implementation ("dpmiload.000" for Jazz Jackrabbit), which fails because it can't control gate A20. This seems to be currently unimplemented in dosbox.
So you'll have to wait until a) dosbox's DPMI implementation gets fixed or b) dosbox allows gate A20 control...
sorry if that was too technical 😉
--Darkstar