yes ...i just installed the 800-900 upgrade....now when i hit the execute button after i select the arrival runway...the dotted blue line turns purple just like it used too....but now it dissappears after a half a second.....without the purple line...i have no way to navigate

Look at your LEGS page after you do this - is there now a Route Discontinuity as your first waypoint? If so, you're not going to see a magenta line because there is no active waypoint for LNAV to follow. Line select a waypoint from the list to the top and press EXEC and you'll get a magenta line direct to it.