A brief note for posterity: if you are getting an error like the following,
X11 connection rejected because of wrong authentication.
xterm Xt error: Can't open display: localhost:10.0
$ unset XAUTHORITY
* * *
The remainder of this post is a followup to my previous post, Stupid Screen Tricks. (The setup I described therein is still alive and well.)
I received the above error when I started a screen session on display :0.0 and (after disconnecting and reconnecting) subsequently tried to launch, from within it, a new X program on a different display (even after setting DISPLAY). The session inherits the old XAUTHORITY value, which, for whatever reason, for as long as it is present, foils attempts to run programs on other displays.
To work around this, I changed my here utility alias to the following,
alias here='unset XAUTHORITY; DISPLAY=`cat ~/.last-display`'
that is, unsetting XAUTHORITY as well as setting DISPLAY before trying to run anything.