CSGCL

If you look at the link below (paragraph 2) it suggests installing csgl.dll either in the libinstall directory or the same directory as your application. So, I'd try copying it to one of those directories before you attempt to add a reference.

csgl.native.dll is a 'native' dll used by csgl.dll and so you won't be able (or need) to add a reference to it. Just copy it to the same directory as csgl.dll. 

http://csgl.sourceforge.net/faq.html#dlls