I fixed the problem by chmod a+s /usr/X11R6/bin/XF86_SVGA (or corresponding server)
WARNING: This could be a security hole!!!
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FreeBSD 4.2-RELEASE i386
6:20PM up 1:36, 4 users, load averages: 1.15, 0.70, 0.32
"The two most common things in the universe are hydrogen and stupidity..."