if you have been moving files around, and your domain file is in your application support file, go to that domain file, get info on it (command i) and check the permissions. if you moved this file from a backup, the file will be locked so that it is for reading only. click the lock on the bottom right, and authenticate it... then change it to read and write.
you should now be able to save... if this was the issue.
hope that helps.