problems with iso.

[Froststep]

I have recently downloaded pcsx. i have been able to run games from cd fine.
recently i downloaded a game from emuparadise(or somewhere like that). it was downloaded in .rar so i expanded it itwas then in .img and i finally converted it .iso with any toliso. however when iever i click play iso it says could not check cd-rom and then when i mount the iso it the wont let me select it. what im asking is whats up with that? im using mac btw if that helps

thanks frosty