This is an issue in Mathematica 10.0.2. It is fixed in Mathematica 10.1.0, but if you don't have access to that version, here's a workaround:
Locate this file:
FileNameJoin[{$InstallationDirectory, "SystemFiles", "Links", "NETLink", "Kernel", "InstallNET.m"}]
and then replace it with the file attached.
Attachments: