For over three weeks this function has not worked in my viewer. The alt / left mouse click function to lock onto objects and cam around them does not work. It won't grab an object, and when clicking on an object while holding the alt key, a white (sometimes black) line bisects the screen horizontally. These are the steps I have taken to try to fix this problem. Uninstalled and reinstalled the viewer several times. Manually removed all sl files and registry keys. (Same problem in any viewer) Updated graphics card, and motherboard drivers. Downloaded all current Microsoft updates. Changed both mouse and keyboard. Computer works perfectly with the exception of this one function. Any help appreciated. Thank you.