VSIX installation error .[PathConflictException: Another extension is already installed to the path that this extension is trying to install...]

One source of this error is when the Author field of the extension.vsixmanifest is left empty. To fix this please give valid author name in the vsixmanifest when developing the extension. It is also possible to extract the vsix and edit the extension.vsixmanifest and repackage it and then try to install. It should work as expected.