OK, interesting development. Looks like the code is correct, but the issue may be lack of admin permissions. To verify this theory, can you please:
1) Run ZIPmagic Studio, from the Application submenu of the ZIPmagic program group.
2) Be sure to run ZIPmagic Studio as ADMINISTRATOR.
3) From the Archives menu, choose the Associate Files menu item.
4) Try to dissociate your ISO extension directly here.
I think it will work, because that's what got it working for me here! If you can confirm this, I will fix the code so the File Associations Control Panel applet runs with elevation, instead of without (as it is right now).
The Next Generation Data Compression Platform