Cubase 5 exporting a song problem

[torqueofficial]

Hey guys, Im currently using Cubase 5 for recording. On my stereo out bus I use Izotope for mastering the song. Now here is the problem, when I listen to the mix inside Cubase it sounds one way, then when I export the project and I play it outside Cubase, it sounds different! (loudness is different, reverb, etc)
Does anybody here have an idea of what Im doing wrong? Please HELP ME!
Thanks! !