So you are using windows 2008r2 or any of it variants and you are trying to connect to a network share in some workgroup.
You get this unspecified error when your network adaptor does not include 'Client for Microsoft Networks', which is often forgotten when virtual network adaptors are created automatically.
- Control Panel > Network and Sharing > Change Adaptor settings > Select your current network adaptor > Install > Client > Client for Microsoft Networks > OK > ... > restart or enable/disable network adaptor