If that's the problem, if I'm not mistaken, FIFA 11 runs on the Next gen gameplay game engine, if you can find a way to make the current stadiums compatible with FIFA 11 it might help you.for new stadiums u need converting from newer games,
something that isnt possible at the moment (however i m trying to find a way)
games wich uses the same fifa 11 engine (stadiums can be copied from here, but all are already added to my patch) :
* fifa 10 (console only) : BayArena, Stade de Suisse, old real madrid stadium
* FIFA worldcup 2010 game : 10 (south africa) WC'10
* FIFA online 3 (old engine only, before ~2015) : Etihad Stadium, BC Place Stadium, Molton Road, 12 Brazil WC '14 stadiums
On the other hand, would the stadiums in FIFA 12, FIFA 13 and FIFA 14 be adaptable to FIFA 11?