If the problem continues, try calling Microsoft.
If you continue to experience this problem, contact the Microsoft Product Activation Center by phone at 1-888-571-2048. It is a toll-free call. There is a way to bypass the robot activation and speak to an actual human, customer support representative, who may be able to issue you a new product key/activation by phone.
This will usually reset the complex hashes that are involved in your activation and causing the issue.
I would also recommend verifying all of your Windows system files have full integrity by launching the command prompt (Start -> Search -> cmd.exe) Right-click "Run as Administrator". Type: sfc /scannow
Just in case.