Drag and Drop suddenly doesn't work with audio clips

Hi everybody ! 

I'm struggling with Adobe Premiere Pro. Suddenly, drag and drop doesn't work for some audio clips. A grey line appeared on some tracks, and when I try to move them, it doesn't work, I can only select them. There's also some white block that appear when I click on the track.

Does anybody had the same problem ? I guess I activate something without knowing... On the screenshot, the A2 track have all those problemes