Probably the last page you were on is email and you have uninstalled the Kaspersky antivirus extension?
In that case (and onyl in that case) login to SSH shell and first reinstall Kaspersky with
# plesk bin extension -i kaspersky-av
and immediately afterwards deinstall it again on the shell with
# plesk bin extension -u kaspersky-av
If your case is different, please open a support ticket with Plesk support so that the issue can be investigated directly on your server.