This comes from a bug in DBP (or a limitation). You can't use make mesh from object on instances. I had to make a replacement command for NGC for it to be able to work with instances. I love NGC's open include file system. You can modify it however you wish to make almost anything possible. The only way I can think of to get it to work with sparky's would be:
load object \"rockwall_01.x\",200
position object 200,0,225,25
sc_setupObject 200,1,2
`create wall along matric perimeter
for l=11 to 13
clone object l,200
position object l,(399*(l-10)),225,25
sc_setupObject l,1,2
delete object l
instance object l,200
position object l,(399*(l-10)),225,25
next l
Or just use clones.