Not sure how many multimonitor users there are here, but I hope there's at least one knowledgeable one

Anyway, I have my /etc/xf86config file set up so when I startx, both monitors have their own desktop on them, and all the programs that I start on either desktop appear on the first desktop. This is fine because I don't have xinerama extensions enabled, but this just shows that both video adapters are set up correctly.

Now, when I do startx -- +xinerama, the X server begins starting up, but then stops and says something similar to "the two desktops have no common display" or something like that.

Can anybody help me based on this? Do you need more information? I'm not at my home computer right now, but I can give the exact error messages later if necessary. Thanks in advance.