Synchronize button greyed out despite tracks being selected

[yumiifmb]

The fix to a greyed out synchronize button normally is to select the tracks (click on V1, A1, etc). But the tracks are selected for me and yet I still can't synchronize. Any idea what I can do to fix this?

[Mike Dziennik]

You can't synchonise multiple video/audio clips at the same time. Try selecting your first audio/video clip and the longer audio clip on A2 then try it.