Plesk: „The System Updates tool is already installing updates in automatic mode. Please try later.“

Package update not possible due to weird error: It seems another update did not remove the /tmp/psa-installer.lock file. The simple solution is to lo in to your server via FileZilla as root and rename or remove this lock file. And you are good to go.

The System Updates tool is already installing updates in automatic mode. Please try later.

More info