I am experiencing this problem, too, after upgrading to U3 on the stable train. I only have a single user (myself). I tried both resetting and changing my password, but it is not helping.
Edit: I have a virtualized server in a DC that I use as a lab and I was able to reset my password there to fix the problem. For some reason, it is not working on my home server, though.
Edit 2: I was able to resolve the issue on my home server by rebooting my desktop. Other computers on my network were able to access the SMB share without rebooting.