"Add side-chain source" grayed out

Dear Cubase-Users,
I’m having a problem with a project, in which I can’t add a side-chain source to any side-chainable plugin. The Button “Add Side-Chain Source” is simply grayed out. No problems with that in an empty project. Is there maybe some project based routing or side-chain option/setting, which might be wrong?
thank you,

One says “farewell cubase” and goes, the other one comes. My first post here. so:

Hello everybody.

Try restarting your pc, launching cubase in safe mode and resetting your preferences. It’s probably bugged instead of a feature.

thx for your reply. that didn’t make a change.
As I wrote: It works fine in other/empty Cubase-projects.

Usually, when the side-chain option is unavailable, it is because, if allowed, a feedback loop can occur : IOW, it’s a safety feature. The fact that you can side-chain without issue in an empty project somehow confirms this.

I would check if there isn’t a potential problem with the tracks involved in my eventual side-chaining routing…

checked that. Couldnt find any reason for a feedback. Wasn’t even impossible on a new Audiotrack with no routing at all. But what I found: I can add a sidechain source on my fx busses and the stereo out, and the sources i can choose are the fx busses. any ideas?