Musescore won't open -just a faulty 'restore windows' dialogue box

Hi
I have been working on a score in Musescore over the last few weeks, working fine.
Then today when I tried to open Musescore, a dialogue box pops up saying:
"The Application "Musescore" was forced to quit while trying to restore it's windows. Do you want to try to restore it's windows again?"
There are two buttons: " Don't restore windows' and " Restore Windows" but neither button does anything. You click on them again and again and yet the dialogue box just stays there.
I am on a Mac os x 10.7 and have even tried deleting Musescore and uploading the new 1.3 version but all I get is the dialogue box.
Please help!! I have a concert deadline for this score looming.....
Justin