Hmm… looks fine to me. Did you get the error after changing or creating the file? Maybe check the file permissions. Make sure the user openhab is running with can access the file.
Was this right away after you had just restarted OpenHAB? Because it looks like a case of items files not being loaded yet when a rule that uses said items runs
And by the way, and I say this with the greatest respect, but the title for this post is really bad. Please consider something a little bit more descriptive other then ‘error message’
I have updated the heading of the post to something a little better
No, openhab had been running for a couple of days at the time. I am not sure what caused this but it looks like some internal error and therefore not something wrong with the rules files.
I will keep an eye on this and see if it happens again.