The Inferno Build let you have more ships, 135 max I believe, but you will loose the Multiplayer Lan/Internet support.
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I would like to know if this is a bug or a limit set in Fred open
It isn't strange that the Limits and errors are mostly set or given at FRED2, when you have a question like that, I suggest you use notepad or an text editor program...., and force an entry that FRED2 would kill or not allow because of "xxxxx not allowed, because special status.......".
I have see this a lot of times, when I get a error like that I just force it using notepad, or either I do most of the mission in a text based file....it prevents error from the FRED2, but it will not prevent errors from you, something that FRED2 does somewhat.........
It may not be recommended, but if you want to check if FRED2 is the problem, then do that.......