You tried to make the conversation as root.
That will not work. Please do it as the site user.
One other thing you must do before you can convert the RRD files, is to create a rule for the RRD storage.
Search for “Configuration of RRD databases of hosts” and “Configuration of RRD databases of services” inside WATO “Configuration of Host & Service Parameters”.
The strange thing is that you can execute “cmk” as root. In a correct setup this command is not found outside of a site user.