Kris,
Probably need a bit more info to help out here. Are these error messages you are getting when you press Save, Test LDAP, or TEST NTLM?
Process should be to get LDAP confirmed working first through the Test button (Top Section of Authentication page), then NTLM configured and Tested (Bottom Section) THEN create an Authentication Policy for the network segments you want to Authenticate. Best practice is to create a test policy for a smaller group first to ensure things are functioning as expected, then roll out to a wider set of IP addresses.
Feel free to contact Support or me directly if you want to go deeper and troubleshoot.