I was able to fix this for one of my Windows 7 x64 machines by uninstalling the plugin (running the Pixelpipe-for-LiveGallery.msi and selecting "remove"), right clicking the installer and selecting "Troubleshoot compatibility", and then clicking "start" in the troubleshooter when instructed to re-install.
However, these same steps did not work for another Windows 7 x64 machine with Windows Live Photo Gallery installed.
Really disappointing that PixelPipe stopped supporting Windows Live Photo Gallery. Seems like that's something you could charge *vendors* for. I use it to upload to snapfish and shutterfly. Seems like they might pay you instead of them needing to build their own plug-ins.