If anyone tried to use MultiMonMan with 3 monitors and it didn't work, try adding:
x := x > 0 ? x : 0
before the line
Gui,%monitor%:Show,x%x% y%y% w%w% h-1,%monitor% - %applicationname%
I can't say this will fix everyones problem, but it fixed mine, somehow 'x' wasn't set so the line sets 'x' to zero if it's not greater than zero.