'unusable report' error message is too generic

[am1r021]

The unusable report error message is too general. It doesn't give any details about what might be wrong with the uploaded coverage file. The documentation gives four possible reasons for the error, but other than that there are few documents available in helping fix this error. It would be helpful if more details were available about this error and/or its causes, or if the API could bubble up any more details with the error message for a user to use in troubleshooting the issue.

[holgerd77]

We would value a response here. 🙂