A sudden thought, is the dialog popping up under a window so you can't see it or it might be off the monitor. This happened with a Gimp 2.8 test I just made. Check on the tool bar for the dialog window. Otherwise back to the answer I had prepared.
I honestly do not know why these scripts do not work on your installation.
The problem could be your 64 bit installation. What I do know is that the scripts work here on a 32 bit Gimp installation both with Gimp 2.6.12 and also Gimp 2.8.0
Going back to your first post. You could try upgrading to Gimp 2.8 and see if that makes any difference.
If you do this, first take some precautions and rename your existing
folder to something like
This is so the new installation does not inherit any previous screw-ups and all your existing scripts, plugins, etc are saved for later use.
You can get a Gimp 2.8.0 64 bit installation fromhttp://gimp-win.sourceforge.net/stable.html
As far as I know this is a combined 32/64 bit installer.
If you want to be a bit more adventurous you can get a Gimp 2.8.1 installation that comes with few extra plugins from Partha. This is a good version (if you like a dark theme
see the side panel and http://www.partha.com/downloads/Gimp-2.8.1-64bit.exe
If you go for either of the 2.8.x versions, run Gimp to make a
folder and copy those troublesome scripts to there. Then restart Gimp.