API Key – error – suddenly registered for another wedsite. . . .?

Hi,

My WP and API key worked well together until last night, and after that hour an error message is showing up every time I try to enter certain WP pages/services.
Error: “Website on http://si……..nu says:
Google Maps API key which is used on this website was registered for another website. You can generate a new key for this website on: http://code.google.com/apis/maps/.”
But I registered the key in question for this WP, and I haven’t changed anything.
The only thing I remember doing few hours before this new error message, was updating the server’s Windows XP with SP3. That update went very well, and I can’t understand that this API messages can have anything to do with that.
But where has my API key gone? When I now try to reenter my key I get the same error message.
I don’t want to get a new API key – without knowing what really has happened to my old one.
I can’t find a place where I can check my key and see what is registered to it – and perhaps edit?

What. . . .?

Eno