external plugins not working

The problem I’ve had for a while is that all my plugins appear in the mix window. However they will not process audio.
I suppose the error warning in the bottom right of all my screens has something to do with it. However, I have no idea what is going on.
Could someone please enlighten me on what I’m doing wrong. Updated to C10 yesterday but I’ve had the same issue with C9.5


I have never ever seen this icon in Cubase. I doupt it’s a Cubase icon.