I'm using a Windows 7 SP1 computer. I only have IE8 installed as a browser and I'm having the exact same issue with the WebRep plugin. It works fine on my other Win XP computers, just not the Windows 7 machine.
From the Internet Security program GUI, WebRep shows to not be instlled even though I installed it during the upgrade installation process. From within IE8, I can click on Tools>Internet Options>Programs>Manage Add-ons and I can enable or disable the WebRep from there, just not from within your program. It throws the above mentioned error every time I try.
Thanks,
Robert