Instrument Track no sound on playback

Probably this has been said before but I have just had some instances of playing a part and the part not playing back - or playing back initially but then stopping for some reason. I thought it was something to do with Kontakt, in which case I would reload Kontakt an go about my business. However it happened to Diva and the reloading trick does not work.

Presumably this is an issue that someone else has noticed. Is there a solution? Is it a bug or is there something I have overlooked. I have spent a few hours trying to resolve this at the expense of enthusiasm for a new project.

I have created a Rack Instrument = no problem???

If you assign a separate midi track to the instrument track does it fix your problem?
See this bug: http://www.steinberg.net/forums/viewtopic.php?f=184&t=53225