I found some code on the net which copies a file and reports the progress using the CopyFileEx API. The problem is that I don't understand how to use it completely, I am stuck at one step.

I have posted the code at pastebin since it was about 100 lines.
http://pastebin.com/7fpGhGBi

So there is one error in that code:
Code:
'void MKV_Chapterizer.AdvancedFileHandling.ProgressChanged(string, string, object, long, long)' has the wrong return type
I don't understand what to do to solve it, I understand that I should change the ProgressChanged to a function which returns something, but I have no idea what it should return, or why it should return anything?

All help would really be appreciated