This kind of error usually corrupts the mission. You can get a working version by changing the format of the backup file(<mission>.bak ---> <mission>.fs2). You can also open the mission with notepad or Wordpad and manually fix it(remove all references to ships 101, 102, 103, n...).
I never had tried editing the mission via wordpad, only the tables... I never thought of editing it like that!
However, I just changed the number of wings to 21, and removed "Gold". The mission works fine now, and there was the error of it being 1 ship too many

Thank you for your advice Mobius, and karajoma, I knew that would be related to the problem.. but thank you for confirming it!
