In my case, I have my installed directory set up incorrectly.
If your solution path is something like "My Project%2c Very Popular%2c Unit Testing%2c Software and Hardware.zip", it will fail to resolve the metadata file; perhaps we should avoid using invalid terms like%2c.
The directory name is URL encoded when a repository is cloned from certain locations. This would convert spaces in directory names to%20, forward slashes to%2f, underscores to%5f, and so forth. However, I'm not clear why the % symbol is causing problems.
My problem was solved by renaming the route to a standard name.