On random occasions and often after a reboot we have problems reconnecting to a UNC path from various Windows 2008 servers. This happens on more than one server and to more than one UNC path.
For example on Server A we attempt to browse to \\sharename and are prompted to enter a username and password. When we enter the correct details we get the error "Unknown user or bad password" If we then log on to Server B with the same account and attempt to browse the same share we get no prompts and can access the share no problem.
I have attached a screenshot of the error we receive. Often a reboot of the server will either cause or resolve the problem which is the strange thing.