Audio output dissapearing

I moved a project from 5.5.4 to 6.5.40, no problems except sometimes when ctrl-moving an event between tracks generates a “serious error”.
So I moved the project to 7 where this does not happen anymore, but often while playing the front channels loose signal. Looking at the meters they show clipping and very loud signal.
Also on 7, I sometimes get audio drop out error while recording 1 mono track.
Restarting nuendo temporary fixes the poblem.

In that project I use FabFilter Saturn x64, Waves 9, Equality. Sound card is RME FF400.

Anybody encountred this?

I moved back to 5.5.4 (rock solid) waiting for a patch for N7.

Thank you.