DLL cant call back into B3D -- or at least no API has been defined to make that possible.
This post might give some clues how to get back from DLL to Blitz:
http://www.blitzbasic.com/Community/posts.php?topic=33997
This post might give some clues how to get back from DLL to Blitz:
http://www.blitzbasic.com/Community/posts.php?topic=33997