Hi, were you using MiniMad version 3 before?
MiniMad 4.0 introduced a new feature that waits for the projector/screen to be ready before starting rendering to address an issues some users experienced. That may be the cause of your problem.
Coming MiniMad 4.1 will add the possibility to enable/disable this later feature.
Waiting for that, if you're in a hurry, you can still flash your cards with MiniMad disk-image version 3 and use MadMapper 3 to export on the MiniMad (all those legacy files are available on Yourspace).