[e-users] screen setup error

I'm just back to using E after a while, using 0.25.4 from Debian sid. 
After first logging in, and every time after resuming from 
screensaver/blanking, I get the pop-up error message: "You seem to have 
no screens configured to be on the given outputs you have. This should 
be fixed by going to: Settings-Screen-Screen Setup."

When I do that, there is a list showing two DP-4 outputs where the 
monitor is connected, and a third that lists the monitor. But the only 
one that I can set the screen setup settings for is the first DP-4. What 
do I need to do to setup the monitor to the output properly?