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):
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