Today I tried to open some existing projects, files I last opened a couple of months ago and on this same machine.  Two of them lock up SPLAT.  One of them results in an Audio Engine Dropout immediately upon loading and in the other project SonarPLT.exe fails immediately.
 
Update:  Apparently due to routing via a Send to compressors, or the compressors themselves, not positive.  On one project a Send to the Waves H-Comp was causing the problem and on the other two projects it was a Send to the Sonitus Comp.  I couldn't open any of those projects to see exactly what was happening, but without those comps loaded the projects open and play just fine.
 
From Safe Mode, without those plugins loaded, I did a Save As for each project.  Each of them opens in normal mode and the playback is just fine, audio and automation in tact!  Thanks:)
 
 

Try opening the project in safe mode (shift+open.) You may find the culprit is an old 32 bit plugin.  

I opened one of the projects in Safe Mode.  I only loaded Cakewalk fx.  No Audio Engine Dropout.
 
The first question was whether to load 'LRS track bus:  GroovePlayer'  not sure what that is.
 
I assume the process is to load plugins until the culprit is found and then do a Save As.  Is that correct?
 
Other than Cakewalk fx I have a couple of T-Racks and Waves plugins.  Izotope Nectar2 also.
 
At first, no audio wave forms were displayed, but after opening the Console View and closing it a couple of times the wave forms appeared.

Got it.  Please see updated OP.

olemon
The first question was whether to load 'LRS track bus:  GroovePlayer'  not sure what that is.

It is the SONAR metronome plug-in. The dll and help file are in "Shared DXi\Groove Player"

Awesome! Glad you got it sorted.