Celtx unexpectedly quits
Presuming that you are using the latest version of Celtx, I think that it's most likely that one of the Celtx preference files have become corrupted. You'll find them in two locations:

Preference file:

/Users/username/Library/Preferences/ca.greyfirst.celtx.plist


Preference folder:

/Users/username/Library/Application Support/Celtx


I'd do the following to troubleshoot:


Quit Celtx. Not a problem, since you can't open it anyway. 
Move the above listed files/folders to your Desktop.
Try to launch Celtx. If things work, great. Celtx will recreate the preferences. You will need to reset any user preferences you made.
If things don't work, I'd Trash the application, redownload it, and reinstall.
After reinstalling, restart your computer before you try to open the app again, just in case anything's being cached


Oh, and best of luck with your script!