Today I reach a greater level of frustration than I had in a long time. After installing Vista Ultimate, eagerly wanting to try out some new Media Center bits, I found I could not connect to a network share. Simple enough I thought, typing in \\WinXP\c$ yielded a password prompt but after the correct password still didn't let me in.
I jumped to the conclusion that some new fancy Vista security 'thing' was stopping my connecting to my XP machine. After wasting almost the entire afternoon and another fews hours in the evening I had nothing. Still Vista would just continue to prompt for a password. I tried separte accounts, enabling netbios, installing updates, anything I could think of even a re-install.
After installing the new Network Monitor 3 and doing a capture I found that it was failing NTLM negotiation, then it clicked. Check the time!!! As it turns out I had the right time, just I was 5 days out....grrr.
So the moral of the story, Keep it simple and look for the obvious problems.