MMM will fail to switch between 2 windows because the ALT key is not held down during the tab during playback. When you record the macro the hold te alt key down and press tab, however when this is played back by MMM it plays back as two consecutive alt+tab. With each alt+tab at playback the alt key is lifted. I have added function key holding to the update list for MMM. To make this work with MMM you are going to have to try a different approach.