Right now I'm using standard Ubuntu 12.10. Often, after using my computer for about an hour, sometimes less, sometimes more, new programs won't open, and I get the error message:
I haven't modified the system in any strange way. I've just kept up with the regular system updates through the software updater, and I've kept my video card driver up-to-date. This just started happening a couple weeks ago.
Maximum number of clients reachedMaximum number of clients reachedError: cannot open display: :0
Out of curiosity, I then installed both LXDE and XFCE, and the same happens when using those DEs as well.
When this issue occurs, if I log out then log back in everything works again for another hour or so, but then the issue reoccurs.