Sorry this is a bug on the Mac version of AC3D.
This will be fixed in the next release but below is a fix for AC3D 5.0.21 Mac OS X.
edit tcl/ac3dhier.tcl
find :
Code:
new_toplevel .hier "Object Hierarchy"
after this, insert:
Code:
if { $ac_platform == "Mac" } {
bind .hier <ButtonPress-2> {event generate %W <ButtonPress-3> \
-x %x -y %y -rootx %X -rooty %Y -button 3 -time %t}
}