The Windows 8 product family has implemented the SMB Secure Negotiate protocol, this requires connections to Windows 8 network shares to be signed or connection will be refused.

This can result in a failure to connect to a Window 8 network share when booted into WinPE. Follow the steps below to attempt a resolution:

1. Boot into Windows 8/Server 2012.

2. Run the registry editor and modify the following entry (create if it does not exist):
KEY: HKLM\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters
Value: RequireSecureNegotiate = 0 (DWORD)

3. Boot back into WinPE and attempt to map the share again.

Further information can be found under Microsoft KB?2686098