If you receive this error “Check the logs for details and correct the problem” when you add RSS Viewer. First you need to check if Kerberos authentication has been turned on. You can follow this link.
If so, following are steps to configure proxy settings.
1. Go to web application directory generally (C:\Inetpub\wwwroot\wss\VirtualDirectories\)
2. Edit web.config using proper text editor like notepad. (I used word pad for editing and lost my application)
3. Search defaultProxy in web.config
4. Change above system.net XML tag as shown below
<proxy proxyaddress="http://:” bypassonlocal=”true”/>