In our network, single domain controller, when some users (members of the domain) request shared folders on the server they are required to enter their credentials, the server is Windows Server 2008 R2, even checking to remember my credentials doesn't work,

sometimes it shows this message: "The system has detected a possible attempt to compromise security. Please ensure that you can contact the server that authenticated you", sometimes it shows different messages,

when I try to recreate the case sometimes I failed, I searched Google for it, I didn't find useful results, some talk about kerberos, but we don't use kerberos,

this keeps going each day or two, how to overcome this, I don't want these messages to appear to users?