Cubase 7 sample rate issue. please help!

Hi there.
I’ve just finished a great writing production session. Me and the artist were both really happy with the track so I went to put some FX on the master buss before exporting but that crashed the project. Wasn’t a problem cause I’d saved it just before… however… upon reopening the project all the music including sample libraries and softsynths play roughly a semitone higher and is fair bit faster. I guess this is a sample rate issue.

I record everything at 48khz 24bit. Both Cubase and my interface say they’re operating at 48khz (as they did when were recording) so I have no idea what’s happened. Can anyone tell me why Cubase is behaving like this?
Thanks in advance

Ok so I’ve managed to replicate the original key and tempo by opening the project in 48khz and switching my MOTU interface to 44.1khz and when prompted pressing ‘allow different sample rates’. But of course when I export the audio it’s sped up as before.

In the short term I just to be able to bounce an MP3 that plays at the proper speed.

But down the line I’ll need the project at the correct speed. any idea how I could backwards engineer this?