solution (of sorts)
It appears that some library parts, are used by Mep Modeler -- with a different icon, as long as I use them
as normal library parts they work fine - If they show a "cabinet" icon then they start looking for a mep modeler key .
Yes, these Library Parts are locked when the MEP Modeler is not loaded with ARCHICAD. This is normal behavior. I think you can unlock them, or unlock their Layer, I don't remember exactly which one. Then you will be able to edit/modify them.
Get Archicad Tips at https://twitter.com/laszlonagy AMD Ryzen 1700X CPU, 48 GB RAM, Nvidia GTX 1060 6GB, 500 GB NVMe SSD 2x28" (2560x1440), WIN10 PRO ENG, AC20-AC26 Loving Archicad since 1995