You were all quite right.

I searched through the whole thing and found the ground trace was incomplete. The condition was no doubt the result of last minute circuit changes made at 1:00 a.m.

I learned several things here with everybody's contribution. First don't panic about fault conditions occurring in the wee hours. Second, it is possible to see Vss floating at 5VDC with no ground and a connection at Vdd. Finally it appears that several PIC's can live happily together on the same bus.

I appreciate the help. Next time I hope the subject of discussion will be a PicBasic programming one.

Allan