While editing a floor plan I'm noticing that group of walls are missing.  no changes to the layers have been made.  If I open the same file in TrueView the drawing is complete...Any ideas what might be causing this matter??Thanks

There can be a lot of reasons... I can´t figure out what's happening but the first thing that come to my mind is:
Are you using hatches in your drawing? If so, try a DRAWORDER and put hatches to Back. Hatch objects may cover other drawing objects and make them "invisible"
Depending on the AutoCAD release you're using, you can do this in a different way by using the command HATCHTOBACK (AutoCAD 2011)
 
Besides, I would try to AUDIT the drawing.
You can also try the following: copy the entire drawing and paste it in a new file. Then run an AUDIT.
 
Hope it works. Good luck