When you save the Web Configuration data, it will verify/validate everything for communication with the web server. The most common cause of this type of issue is simply a missing or incorrect piece of data. I'll list the ones I see most below:
Is there a DNS entry for the Web Server? Must have forward and reverse lookup zones configured.
Are you using TLS/SSL communication? Check the following:
Certificate "Issued to:" field exactly matches the Web Server name.
Root certificate is in Trusted Roots on the SEE server. Alternatively, you can add the communication certificate itself in the Trusted Roots folder on the SEE server.