Fit Improvisation needs a sacrificial guide track that has one and only one MIDI event on every quarter-note beat. This track can be created from a copy of your recording, but it does take some time to do that, and can be problematic if the recording doesn't have an event on every beat. There's also a 3rd-party app that a forum member wrote that does essentially the same thing, but allows using smaller beat divisions:
http://forum.cakewalk.com...vailable-m2832233.aspx Another option is to render the MIDI to Audio using a patch with a nice fast attack and decay (or even a drum synth), and use Audiosnap to Set Project From Clip.
Or - my preference - use Set measure/Beat At Now to do it manually, setting as many or as few points as necessary to align the timeline to the performance.