could you please provide a screenshot of this pop-up? It would be even better if you could provide an URL to a site demonstrating the problem.
Also wouldn't it be better for you if the pop-up didn't appear at all?
article describes how to configure your IIS app to trust all certificates.
Also, in IE this might resolve the problem:
Click on Tools-->Internet Options
Go to Advanced Tab
Scrolled down to "Check for publisher's certificate revocation." and unchecked this.
I hope this helps - hope to hear from you soon!
All the best,
the Telerik team