I was tweaking the bed size for my MP Select Mini, and when i set x/y to 125 Cura refused to slice, saying that the prime tower X/Y positions were invalid.
Changing the dimensions to 124x124 fixed the problem. Interestingly, 125x120 was working just fine as well.
FWIW, i couldn't adjust the prime tower positions because my printer is single-extruder, so those options were hidden.