It appears there is an issue with the CURL installation on that site. I have created a demo page here you can see the error it gives:
Please show that page to your hosting provider and they should be able to use it to solve the problem.
The issue is that the powerCMS code is trying to verify the serial number and it is failing because of the underlying CURL issue. It only verifies the serial number once per month once it is verified, but if it fails it keeps trying every time someone visits the site.
I've now updated it to mark it verified for this month, so that you won't have the slowdown again until march. That should give you time to fix the underlying issue. If your hosting provider fixes the test page before march then it won't be an issue any more moving forward.