Cubase users help!

pikachu69

mixomatic 2000
Jun 7, 2010
593
0
16
New Zealand
I have Cubase 5.
I do all my mixing in Cubase. I mix down then re import into a new project to master.
When I get to pushing the master level up I can hear a very obvious clipping/distortion appear even though it is no way near too loud (round -10rms usually), and once the track is mixed down (even though it distorted listening to it) it sounds fine apon playback, no clipping. Even if I bring it back into cubase to listen it sounds fine.
So the clipping is happening in Cubase while im mastering its not the signal itself. I can run the same mastering plugin chain in a different program and it sounds fine. This is a new problem since moving from cubase 3 to 5.
I have always used cubase (I still have the original dongle and box from SX 1.0) but this is really annoying and I cant see what may be causing it.
Any ideas?

Cheers.