Ok, if you can believe what you read on the internet, it appears someone else out there also believes it is a known Python issue on Windows.
Please try my suggested workaround of moving your Calibre config directory and let us know how you got on. Once you confirm this works I will add some notes to the introduction to plugins sticky thread. It appears this issue will only affect international users on Windows who either have accented characters in their user names, or have a translated installation of Windows.
I think the reason why Loeffel got it working in the end on the "Generate Cover" thread had nothing to do with Calibe reinstallations, but more to do with him eventually installing the plugin from a directory that did not have accented characters in it. I would also guess that they have a different international settings of Windows on their machine to you, which does not have an accented character in whatever the translation of "Data Applications" is if any. It would also explain why the user on the Kindle Collections thread never reported any success.
Other than rewriting all my plugins to not use ZipImporter, I don't think there is anything else I can do at this point. I am at least stoked to have gotten to the bottom of why this occurs for some users.
EDIT: This is what happens when you take too long to type a post. dwanthny posts in-between and makes me look like a repetitive idiot