Convert to grey-level - what does it mean?

I have imported video footage, then I tracked plate and imported image, and while I importing image, I see this:

This means you imported a matte clip. Matte Clips have to be in grey scale to work correctly. If you want to import an insert clip, use the insert dropdown instead.

Oh yeah yeah I see now, I was tried to insert AlphaClip.
Okay I gonna fix it now, thanks Martin :rolleyes: