Symptoms
You can not add .dll file as a reference in Visual Studio or SecurityException is thrown.
Solution
Most likely the problem is a protection on files coming from other computers. You just have to open file properties and click on Unblock button. Unblock the zip file first, and then extract the dll, unblock the dll if needed:
Other tricks is to copy the file to a file system that doesn’t support alternate data streams, that slices them off the file. A flash drive for example.