Just another theory . . . I ran across another thread stating that custom calibrated monitors can cause problems. (I use Color Eyes Prio)
Keynote, or PowerPoint uses that custom monitor profile for the LCD projector as well.
Temporarily switching the monitor calibration back to sRGB will avoid profile conflicts.
Thanks for the feedback.
Since there doesn't appear to be a Mac-Dell compatibility issue, I might just pick up a second DVI-VGA adapter.
It still seems strange that everything worked well at home, and not at the convention.