0x80004005 Error browsing network share

Hello,

I have a Windows Server 2003 domain and several Vista PC's and a couple of
XP PC's. There are some shared folders on the server and on several of the
PC's. Most of the PC shares are for media files. On two of the Vista machines
I'm running in to this problem on, I have recently upgraded to SP 1. However,
this issue was apparent before SP 1 as well (I was hoping to solve with SP 1).

Repro is:

> Browse share: \\computername\share or even \\computername\C$
> After some wait, prompted for password
> Enter password and it says that those credentials were already tried
> Click cancel to password prompt and get:

Windows cannot access \\computername\share
Under Diagnose button:
Error code: 0x80004005
Unspecified error

The target machines are on and I can access the internet and shared network
printer.

Here is the strange part:
I can go to the target machine and log on and I can access the source
machine I was just at.

Or, on the source machine, if I log out and back on, I can then access shares.

So, it seems that my credentials have somehow expired or something. Does
anyone know if this is something I need to address on the client or the
server and if so, what?

thanks!