Right tested it again. It absolutley 100% works on a file I'd originated in Prelude CC and then worked on in Premier CC and After Effects CC and Encore CS6 saw it, loaded it and did what I wanted with it no problems. However, I just originated a file directly in Premier CC did minimal work on it and tried to load it into Encore CS6. En saw it and was happy to attempt to load it but froze half way through the process.
Could somebody else please try the 1st method and see if it works for them. In theory it shouldn't make any difference since the file is a Premier Pro project file saved by CC, but originating in Prelude seems to have made a difference!