From the IIS 8.5 STIG, "The production IIS 8.5 web server must utilize SHA2 encryption for the Machine Key....
Click the IIS 8.5 web server name.
Double-click the "Machine Key" icon in the website Home Pane.
Verify "HMACSHA256" or stronger encryption is selected for the Validation method and "Auto" is selected for the Encryption method.
Before I go clicking that, does 10.7.1 support that level of encryption?