Hi guys,
Sorry about the 'cloak and dagger' stuff but my problem was that I could not move any naval units between cities nor select them to build in the harbour. I did not want it to be widely known as it would have given others a incredible opportunity to clear my docks.
Also, I could not att or supp other cities as the graphics in the pop up window were not showing so I was unable to select units there too. :/
Thankfully it has now been resolved (over 8hrs in after reporting).
DG