When attempting to attach to a C$ share with proper credentials, it may be rejected as “access denied.”

Example: \\machine\c$

On the target machine with the desired C$, Add/change this registry key and restart the Server service.

Key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
 Value: LocalAccountTokenFilterPolicy
 Data: 1 (to disable, 0 enables filtering)
 Type: REG_DWORD (32-bit)