I've looked at your code samples, and i added a script file with the OnClientFileOpen and referenced it through the <head></head> tag of the page (the reason being that i'm using a sitefinity website, and the FileExplorer is inside a user control).
This is how i then modified the FileExplorer to look like:
The problem now is that the files are no longer shown. By deleting the OnClientFileOpen property the files are shown again. Any help would be appreciated.