I can't move imovie clip

I know I could do this before but not now... I'm trying to grab a clip from the event library and drag it up to the project but no go. A hand appears at the mouse pointer but it doesn't function... the clip will not move. I can only click the Add Selected video to project button. The video goes at the end of the project and I want to insert it between some previous clips. Please help- I've searched help, I've searched the web...