Hi Tim,
I wasn't misinterpreting the message, I was following it's advice.
First I got NOT realtime because "project colour working space is on" so I turned off "Use Display Colour Management". Then i got NOT realtime because "zoom is not 100%" which I corrected, then I got NOT realtime because "project colour setting is 16 bit". I duly converted the project to 8 bit and all was well. So I assumed that 16 bit project setting was causing issues, I also tried 32 bit as well with same results.
Since having discovered the converted/unsaved issue I have to say it is strange and not a behaviour I have seen with AE before and I have been using it since it was Cosa Effects!
I have tried various projects and the culprit seems to be anything that has live actionesque video in it. I have a project that has a slow subtly changing graphically created BG (imported QT file) that played fine without saving but the next one had fast moving treated flames as a BG layer (imported QT file) that suffered the "Not realtime" issue. The original problematic project had several layers of AVID mxf footage in it.
One thing I have noticed is that you can no longer tell AE not to mirror the RAM preview on the computer monitor at the same time while using the Video Preview function. This always caused playback issues in the past so I always told AE to use the Video Preview only which helped. Could we put that back or does that not work anymore with the Mercury Transmit Preview?
Anyhoo, most initial problems are now solved and I am nearly ready to switch over to CC 2014. Just waiting for a major project to finish and then .....
thanks for all the advice
Nic