Desktop effects gone - "Desktop effects could not be enabled"
I didn't touch any setting, but my desktop effects are gone. I may recall that they stopped working between two ubuntu updates. A glimpse in Synaptic Package Manager shows that the proprietary nvidia drivers (I am using an nvidia GeForce 4200ti) are there. However when I try to enable "extra" effects, I get the "Desktop effects could not be enabled" message (I am not using Advanced Effects Manager, just the plain one default).
How do I troubleshoot this?