I recently installed Windows 8 on my business laptop and discovered I had problems connecting to certain networkdrives.
The solution was adding the following DWORD (32-bit) Value in the registry.
Create DWORD (32-bit) Value: RequireSecureNegotiate with Value 0
This should solve the issue.
If this doesn’t work you can always try to run the following command in PS (run as admin):
Set-SmbClientConfiguration -RequireSecuritySignature $true