iMovie buggy as hell - help!!

I'm using iMovie to edit a project, which needs to be in very soon. I have done loads of work on it and it seems to have developed some weird bugs. Now when i try to render titles and go to 'add', they appear in the timeline, but the red progress bar just stays static and the clip wont render at all. Also some of my clips become greyed out, and only can be used again after restarting iMovie.

Does anyone have any suggestions or has anyone experienced what I'm talking about?

Thanks

 

thanks very much that worked