Verify that the Raiser's Edge Web Server domain has a valid SSL certificate.  This can be viewed using the SSL Shopper.
If a valid certificate is not found, this must be resolved before proceeding.  

If the SSL certificate is valid, and bound correctly:

Try each of the following steps in order until the issue is resolved:
1.  Verify Port 443 is open
2.  Restart the application pool in IIS
3.  Restart the server
4.  Repair IIS
5.  Re-install IIS