Same problem here.
This thread should not be marked as solved, as we seem to be quite some people here having the same problem, and restarting OpenHab does not solve it.
Agreed, Done!
Add BasicUi tag as well, as it seems to be an concern of the BasicUi.
I dont ssee the error when IĀ“m not connected to BasicUi. But as soon I connect to BasicUi and klick on any sitemap, I get the error. Everytime.
What about ClassicUI?
I havnĀ“t tried, as I only use BasicUi, (dont even have classic installed).
Just tried HabPanelā¦ It gives the error as well. So I guess classic Ui will as well.
Would you mind installing it and trying, please?
Then post the error with the few lines before and exactly what you do on the UI to make the error happen. Then I can take that to gitHub.
Hmm installed Classic Uiā¦ Not without problemsā¦ Anyway itĀ“s running, and not given the same error.
But I only see my āhomeā site, and not all my sitemaps ? Is this normal?
Hmmā¦ Weird!
I ran openhabian-config from a console (Putty),
Executed the āinstall needed and recommended system packagesā.
Rebooted my Rpi3 (have done that tons a times lately due to other errors).
Now I dont get the problem anymore. And I canĀ“t recreate it either.
IĀ“m running openhab 2.2 stable release.
Mark your post as solution, please
No can do. The problem returned last night.
I entered paperui and system configuration, did a small change regarding the country code. Bam! The problem was back. 
This starting to irritating me. I have a feeling it may be due to faulty SD card.
If the problem goes and come back and you are starting to have erratic behaviour then yes probably.
How long has that SD card been in there?
As far as I can remember, since June/Juli last year.
Could well be.
Didnāt know you were running on a PI. One of the reasons I moved away from them.
I still use them but for little apps around the house, not for the heart of OH.
I have yet to decide what else to use. I have several computers running here. I chose RPi due to the hasslefree installationā¦ Actually my first go with Openhab was on my windows server. I gave it up and gave Domoticz a try. Few weeks later I went back to Openhab, going all-in on a Rpi3. Now IĀ“m kinda stuck on it untill I find an decent replacement with a hasslefree setup, as IĀ“m no good a linux in anyway 
I have given up with windows and I am not looking back. The learning curve was steep at first but linux is very powerful and far safer than windows.
It doesnāt seem that this error on OH is breaking the system. So keep monitoring your system and look for a replacement.
I will.
just need to figure out, how to install openhab without using the hasslefree SD card image.
Exactly same issue on my 2.3.0 snapshot version.
i have the same issue on a manual installation on debian
Well, it seems like my message #27 do seem to do something. I did it once again last week. And I havenĀ“t seen this error sinceā¦ (knock on wood).
If you are using a Pi 3, you could move to hdd. Had a 2.5" lying around, bought a 10 euro cable and cloned the sd to the hdd. (after setting the usb boot option).