Not sure if it’s a coincidence, but ever since my pull request was merged this morning (#44 Fill Background Path), I’m getting this error when I go to Window > Plugin Manager:
The operation couldn’t be completed. (Problem parsing repository source error 123.)
The double quotes in your description needed to be escaped. Running plutil -lint on the file to check for syntax errors would have caught that. I submitted a pull request that fixes it and adds a note about using plutil to verify the file. When @GeorgSeifert merges in the change, the Plugin Manager should work again.