Assuming it is a Microsoft Office application that is requesting a product key: Please review:
Invalid product key type errors occur in Microsoft Office 2007 or 2003
Otherwise:
In order for us to analyze and troubleshoot a non-genuine notification issue you may be experiencing, please download and run
the Microsoft Genuine Advantage Diagnostics Tool.
After running the tool, click on the Continue button, then click on the Copy button, then Paste the report into your post.
Also, please include a brief question or pertinent background information that would be helpful in our endeavor to assist you.
Thank you!