About two weeks after I upgraded my Mac Mini to Yosemite I woke up one morning and kept getting the following prompt's from my PC when connecting to my mini: I have never had a problem connecting to this mini before. They are members of the same homegroup (workgroup), SMB sharing is turned on for all accounts, the permissions are set correctly and very liberally, I have checked with firewall on and off and performed all necessary tweaks. I've tried changing the domain by entering the computer name\account name, the workgroup name\account name, nothing will be accepted. I've checked and rechecked passwords, created new accounts, nothing seems to be working. The mini still connects fine to the PC, but the PC cannot connect to the mini. Both computers still connect fine to my Macbook Pro. I've made sure there are users on the machines with the same account name, I've even created a new account with new credentials and it still won't connect. I've gone into windows administration tools and deleted credentials and built new ones, nothing seems to work. As best I can see either the PC is holding onto some corrupted credential information, or the mac has switched something that I cannot find to save my life. Does anyone have any suggestions at all?