I am currently working on extensions for TFS2012 web access. This was an error I received when trying to upload an extension. For those with admin access to their TFS, you can access the extensions page at http[s]://tfsserver:port/tfs/_admin/_extensions.
I could not find a solution online, and eventually figured it myself. Although it didn’t make me smart, but rather made me feel dumb considering how trivial it is.
The solution: Make sure the directory of your files is set up correctly before zipping it! And by that, I mean have no directory at all. You cannot put the data files in a folder, and then zip that folder (which is how I usually zip things). You must zip the files directly, with no folders in-between. In the zip must contain at least one .js (or .debug.js) and a .min.js file associated with it.
I hope no more explanation is needed, and this has helped someone.