Problem:
A Windows 7 Home Premium 64 computer could not access a Windows 2000 shared files.
Solution:
After some search on the Internet, I realized that this was a common problem with Windows 7 Home Premium computers. Luckly, some people already figured out a solution. You need to update Windows 7’s registry to add a key/value pair.
You type REGEDIT.EXE in run box. Then navigate to: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
Add name: LmCompatibilityLevel and set its value as 1.
See the picture below.
Reboot your computer. When it starts up, you can access your shared files.
Reference: