Max routes problem

[aland]

I had 41 flights between two airports and still did not fill the demand. I was using a 737-200Adv as the runway was not big enough to use a bigger aircraft. I have begun retiring some of my 200's and replacing them with 300's. When I changed each route to a 300 model I got a message saying that I had exceeded the maximum amount of flights allowed between airports which is 40 flights per day. I have four flights per aircraft per day and when I changed the aircraft type on two planes It would not allow me to schedule any routes even though I now only have 33 routs. Has this happened to anyone before and if so how do you fix it.
Thanks