I get this error message whenever I try to initialize any Gn* object. Specifically for GnManager, I am using the path that contains the gnsdk_csharp_marshal.lib file from the SDK and a filename that contains the license string specified for my application in its entirety (beginning with "-- BEGIN LICENSE" and ending with "--\r\n"). The license string file is in the same directory my application is running from.
My instantiation therefore looks like so:
GnManager manager = new GnManager(Directory.GetCurrentDirectory()+"\\lib", "license.txt", GnLicenseInputMode.kLicenseInputModeFilename);