Get in touch with your IP, and get them to deal with it. Fear not though, you should be able to get this overturned and removed from your credit file - as your IVA supercedes a CCJ.
If it was me, I would also call the court and tell them about the situation, and seek their advice - just incase the IP doesnt do anything about it.
The whole process of CCJ's is fairly automatic I think, and I suppose that is why this is happened. I think creditors/DCA's/Solicitors can even apply online, and they probably instigated proceedings before your IVA was approved and just havent bothered dealing with it since. As you never responded to the courts, the automatic process has come through to this final judgement.
I suppose there is also a slim possibility that the CCJ papers are fake, in which case a call to the courts would be recommended, just to make sure you know where you stand.
I also have to add, this is just my opinion and what I would do... I'm no expert, just another debtor..
