Help! Unable to create enough vehicles

I made a really cool park that took alot of time, but now when I try to open new rides, it says "Can't open _____, Unable to create enough vehicles." It isn't that I have too many rides, because if I close one and try to reopen, it gives me this same message. I don't know what this is and I want to fix it. How do I fix?
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Bull rides: 81
Shockwave rides: 55

Are you using a trainer? Might be a problem with that, if so.

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Po!nt of View: A different look at Roller Coasters.
http://www.crosswinds.net/~justmayntz/thrills/

I had this problem, and unfortunately, I only found one way to fix it. Download (or use if you've already got it) TRG's Swiss Army Knife Trainer. Perform a "Neutron Bomb" to nuke all the people. Your rides will still be in tact, but all the guests will be gone. Then, just reopen the park and wait for them to populate it again. This worked for me when I had the exact same problem with a huge mega-park I made.

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Jman
Webmaster: Gravibulb Coasters
http://balder.prohosting.com/gravbulb/coasters/

I'm not sure on this, but I think it has to do with how much RAM you have, which I think is has a direct relation of how many sprites you can have.
I'm almost certain it is that, and you computer just can't handle making any more sprites for the game. There is no way to solve it other than find a way (such as Jman's sugestion) to remove some sprites from the map.

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Do your own homework!