I have had the same problem with my PPC 6700 running WM5 and WM6.
I have installed the HTC Network Plugin CAB. I can see the servers on my network (all thru WIFI). When I select the server, it prompts me for my user ID, Password, and Domain (click save password). I click OK and it comes back requesting login info again and again and again.......
I have the same issue from Pocket File Explorer when I open a path to the //server/share!!!!!
I have a Dell X30 running WM 2003 SE and I can access all of my shares with no problems on the same network!!!!!
What am I doing wrong?