Can't update Scrivener. App store says I use the wrong ID - I don't!

So, I can see Scrivener in my list of purchases. It says "update", but when I click it I get the message that I'm using the wrong ID - please login with the correct ID and try again. The thing is, I only have one ID and I still have the receipt for that app and it says it was bought with my current ID. What am I doing wrong?

It was bought back in December 2011, and I might have updated my account since then, but surely it would count as the same ID?

Thanks!