Hello James,
When you have authentication problems, you can perform a connectivity test to check for connectivity issues. You can enter the hostname or the IP address of the network device that you are trying to connect with and execute the following commands from the web interface: ping , traceroute , and nslookup .
For step by step process, please go through the following link:
http://www.cisco.com/c/en/us/td/docs/net_mgmt/cisco_secure_access_control_system/5-5/user/guide/acsuserguide/viewer_troubleshooting.html