Comment 4 for bug 430121

invoke-rc.d is not supposed to be failing in these circumstances - policy documents that the 'start' option to an init script is supposed to return success when the job is already started. And since this bug was first filed, upstart-job has been fixed (in upstart 0.6.3-4) to implement this behavior.

So I think this bug is already fixed elsewhere, and in any case ignoring errors from invoke-rc.d would be the wrong thing to do here - anything causing invoke-rc.d to fail is a bug somewhere else that needs to be located and fixed.