I had similar issues a while back and still do when I go into A7 occaisionslly and the only way I have ever found to sort the prob is to rebuild the entire level from scratch under a new name though sometimes 'save as' has also helped get past this point.

In short, I think the project files are corrupted by an initial mistake or your script is seriosly in error somewhere.

Then again, are you using templates or not? if so, you could have 'includes' in the wrong order.