Ulrich G. Kliegis
It seems it took Tobi Oetiker, author of MRTG, two iterations to get this bug
fixed. No more error messages now with version 2.17.2, tomorrow I'll try to
achieve a contiuous operation.
So, after all, all is well.
Thanks to David and Giuseppe for their "quality time", as Tobi put it for the
time he invested in debugging.