arc stopped working

[Peter Trommler]

Hi *,

I am getting the following error message from arc:

peter at montebre:/local/home/peter/ghc> arc diff
Usage Exception: Failed to load phutil library at location '/local/home/peter/ghc/.arc-linters/arcanist-external-json-linter'. This library is specified by the "load" setting in ".arcconfig". Check that the setting is correct and the library is located in the right place.

I looked at '/local/home/peter/ghc/.arc-linters/arcanist-external-json-linter' and it is an empty directory.
`arc upgrade` did not fix the issue.

What can I do to fix arc?

Thanks, Peter