Edit: I just tried this again without any permissions issues. Who knows with Windows 
The essentials: Move the C:\Program Files\GIMP 2\lib\gimp\2.0\plug-ins\script-fu folder somewhere safe
Replace it with the script-fu.exe file
Not being a Windows user a bit of a struggle. I could be wrong but it looks like a permissions issue. You could try this:
Using the old (not samj version) from http://gimpchat.com/viewtopic.php?p=146955#p146955
1. Find the gimp plug-ins directory C:\Program Files\GIMP 2\lib\gimp\2.0\plug-ins
2. Right click on it
3. Open the properties
4. In the Security tab select Users
5. Click on Edit
6. Click in Allow -> Full Control (Modify enables as well)
7. Apply (wait a second while that works) and then OK to back out.
8. Properties should look as screenshot, OK that to back out.
9. Into the Plugins folder C:\Program Files\GIMP 2\lib\gimp\2.0\plug-ins and move the whole script-fu folder somewhere safe.
10. Move the script-fu file into the plug-ins folder.
works here
The essentials: Move the C:\Program Files\GIMP 2\lib\gimp\2.0\plug-ins\script-fu folder somewhere safe
Replace it with the script-fu.exe file
Not being a Windows user a bit of a struggle. I could be wrong but it looks like a permissions issue. You could try this:
Using the old (not samj version) from http://gimpchat.com/viewtopic.php?p=146955#p146955
1. Find the gimp plug-ins directory C:\Program Files\GIMP 2\lib\gimp\2.0\plug-ins
2. Right click on it
3. Open the properties
4. In the Security tab select Users
5. Click on Edit
6. Click in Allow -> Full Control (Modify enables as well)
7. Apply (wait a second while that works) and then OK to back out.
8. Properties should look as screenshot, OK that to back out.
9. Into the Plugins folder C:\Program Files\GIMP 2\lib\gimp\2.0\plug-ins and move the whole script-fu folder somewhere safe.
10. Move the script-fu file into the plug-ins folder.
works here