Nokia 6600 and Java Problems

I have downloaded some .jar games and they install without any issues however when opening it shows the opening screen (turning white and game company logo) and then reverts back to the previous screen. Does anybody know why this is? Is it incompatibility? Thanks for any help in advance! __________________ It will most prob be coz the .jar files are for a series 40 phone (6100, 7250 etc). The larger the file the more likley the game will play on 6600.