Still on Win 8 because I read that 8.1 was causing problems.

OK!!!!!!
 
I think I found the culprit.
 
By a series of trials and errors, I was able to discover that it was my QL Spaces reverb plugin that was causing the issue.  If I removed the .dll file from the VSTplugin folder, it would pop up and let me know it was missing, but would load properly otherwise.
 
I can't wrap my head around how\why though.  When disabled, I can get into the project just fine.  Earlier, I was able to re-load it into the project and it worked perfectly.  It just wouldn't open again once the project was closed.
 
I'm going to try to re-install it.
 
Thank you everyone for your help!

Yup 8 times out of 10 plugins... good on you... Guess you will be contacting EastWest support (apparently my favorite forum that I've never been to!). This simply demonstrates that just because somebody is having similar symptoms, it doesn't necessarily mean that they are having the same problem.

I had a very similar issue.  It turned out to be voxengo glisseq that was messing things up.  Glisseq had never caused me any problems before, so it seems like there was a change in the x3c update that brought out some conflicts with plugins that worked fine before.
 
Glad you figured things out.

I use QL Spaces on every project and I haven't had any trouble. I love that reverb. not sure I could live without it. I hope u get it worked out!