A quick read of the DM556s manual may help:


There are two LED lights for DM556E. The GREEN one is the power indicator which will be always on generally. The RED one is a protection indicator which will flash 1-2 times in a 3-second period, when protection enabled for a DM556E. Different number of flashes indicates different protection type (read section 11 for detail).

There are two protection types, a single flash means over current protection and two flashes means over voltage. I'd start with looking at your current limit settings and making sure they're appropriate for your NEMA 23 motors rather than your NEMA 17 ones.