So I have a simple vessel with a cfg and a mesh. I use attachment manager to attach the arm to the vessel. Exit and get a ctd.
here is a link to the vessel and scn.
https://drive.google.com/open?id=18HTLyZ8NO2xhpB7s7HsNYqQubO7TEpVb

Code:
; === Configuration file for vessel class ===
ClassName = logistic
MeshName = logisticmodule
Mass = 100
Size = 7
BEGIN_DOCKLIST
0 0 4.697 0 0 1 0 -1 0
0 0 -4.697 0 0 -1 0 -1 0
2.127 0 -1.512 1 0 0 0 1 0
-2.127 0 -1.512 -1 0 0 0 1 0
END_DOCKLIST
BEGIN_ATTACHMENT
C 0.0 2.271 -4.217 0 1 0 0 0 1 arm
END_ATTACHMENT
TouchdownPoints = 10 0 5 -10 0 5 0 10 5
here is a link to the vessel and scn.
https://drive.google.com/open?id=18HTLyZ8NO2xhpB7s7HsNYqQubO7TEpVb