PT 11.3 hangs on Avid Video Engine during launch

[New Hope Media]

I've just installed PT11.3 on my Mac running OSX 10.10 Yosemite.
First let me say I've been running PT11.2.1 on Yosemite without any problems for the last two months.
However after installing PT11.3 when I open an existing ProTools session containg video I get a message that the AVID Video Engine is loading ... well waiting to load... but it times out and all I can do is load the session with the Video Engine OFF and, hence no video.

I'm not running any external video hardware, just displaying my video on the desktop.
I am running an older, non supported AVID 002R but it is working, and has been all along, with PT11.

My System is:
Late 2013 Mac Pro (dusbin)
MAC OSX 10.10
AVID 002R
PT 11.3
10TB LaCie Thunderbolt RAID