Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
 
public static extern String hdGetErrorString(uint errorCode);
 
The C/C++ Equivalent is the following:
 
 
HDAPI char * HDAPIENTRY hdGetErrorString(unsigned int errorCode);

I run it by saying this:
            System.Windows.Forms.MessageBox.Show(HDDevice.hdGetErrorString(515));