This is one of the issue, which was scratching our production support team's head for a long time, today we found out the resolution.
When we try to add a new sharepoint list item in sharepoint 2013 environment, we get the error popup is "The server was unable to save the form at this time. Please try again."
- Edit your web.config of your sharepoint site
The path location is
Drive\Inetpub\Wwwroot\WSS\VirtualDirectories\<port number of your web-application>\web.config
- Add the entry
- Save the changes
The issue is resolved. we are able to add sharepoint list items with out any issues.
Happy SharePointing :-)