Activation Key Not Authorized for this Server...

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I'm having trouble getting started. I activated the plug-in with my key. Started playing a bit with the widgets and all seemed fine. I came back this evening to start customizing other pages with shortcode and suddenly there is something wrong. My diagnotics area says: "Activation key authorized for this server? : No "
Any recommendations? I only have one blog - though there are several domains pointing to it....