Same problems here dmackenzie...have also launched a question but no answer so far. Also the phone help lines closed till Monday so looks like its a frustrating weekend.
Spent 4 hours yesterday trying to fix this with tech support. It seems that you needed a 1 gig video card and mine was only 500mb. Created a new user on my Mac to turn off the video card but could only use Lightroom CC with that user. I was going back to LR5 but noticed that there was an upgrade for LRCC this morning (April 30). Seems to have fixed the issue as it now opens without the video card turned off.