It wos quite hard but I found the problem.
This is what I have done:
- Stop openHab
- Backup addons.config and dashboard.config from /var/lib/openhab2/config/org/openhab/
- Delete original files addons.config and dashboard.config
- Restart openHab
- Go to http://myserver:8080
- Select Standard installation, at this point both files are recreated
Checking the two files recreated i found that:
- dashboard.config have one line more than the previous one
- addons.config have only few lines compared with my old one but i noticed that the ui line was different:
this is the old one,ui="basic,paper,habpanel,habmin"
this is the new one,ui="dashboard,basic,paper,habpanel,habmin"
Then I stop again openHab reinstall my old addons.config file with the correct ui line and restart.
Now the error is gone.