Here at work our "My Documents" are stored on network storage, so its actually on \\someserver\somelocation\My Documents\
Some plugins that use java, or just plain ..some plugins. Don't like/trust paths like \\
The solution here was to create a folder like c:\vs-addins\ and dump all my custom addins in there instead, and then add that folder to the visual studio addin paths.
Download the vsix, open it as a zip, and take the files from inside and place the in for example your folder c:\vs-addins\chirpy