i read this on the x11vnc page, http://www.karlrunge.com/x11vnc/
"No problems like this have been observed with Windows VNC Viewers: they all seem to keep their entire framebuffer in local memory. Gotcha for KDE krdc VNC Viewer: One user found that KDE's krdc viewer has some sort of hardwired limit on the maximum size of the framebuffer (64MB?). It fails quickly saying "The connection to the host has been interrupted." The workaround for his 1280x1024 x11vnc-side display was to run with "-ncache 10", i.e. a smaller value to be under the krdc threshold."
however i don't find ncache as an option in my x11vnc... so i still have this problem, but it only occurs when i don't use the high quality setting on krdc