Thanks heaps for your reply David. I frequently google Logic pro question's which then lead me to this site and more often than not i happen upon your replies, which have helped me dozens of times, so thank you.
Okay, error -42 = too many files open error, good to know.
Yes i do have a couple other apps open, a word processor (WriteRoom) and usually an internet browser (Firefox).
It is the only Logic project open.
I haven't tried seeing if the project works in a new user account, ill try that.