Okay, after several hours of searching, now that I posted this thread I found someone with the same problem on creativecow
This workaround works
"I eventually got around it by importing the entire timeline into a new sequence. It is really weird as I all of the settinsg appeared the same in both yet I could write to one and not the other."
but it doesn't explain the problem.
Anyone has a guess what it could be ?
I'm not sure if this is a similar situation, but might be worth looking into. To record just analog audio in an HD project, I need to create an SD sequence and use my DVCam deck via S-Video In for a synch source. I haven't tried, but If I plugged in my HD camera for SDI synch it would probably do the trick with an HD sequence. I'm in Win 7, CS5.0 with a Matrox MXO2 LE Max for I/O, so I don't know if it's a Matrox thing or not.
I find that Soundbooth performs this function far easier than PP does.
I wonder if that same applies to Audition.
The "workaround" did not realy work out.
After some testing I found out that it has something to do with the Audio-Reverb function in subsequences.
Somehow you can only use a limited amount of reverb effects in one subsequence.
If you take the whole subsequence and put it in the main timeline it functions quiet well.
Or just erase one or two of the reverbs.