FFXI(PC)-Character DissapearenceFollow

I recently purchased ffxi for PC. The problem I keep having is characters just disappear of the screen. Both PC's and NPC's disappear when I move the camera around at all. At other times the flicker rapidly. When in an "invisible" state you cannot select them. I am also having a problem with screen flicker whenever the sun is in view on the camera the screen flashes yellow, with more intensity when the sun is directly on the screen, even if it is below the ground it appears through the earth. Any help would be much appreciated.