My specops are loaded with inq + bas weapons and use bas models (with permission, this addon is not publically available) that's where that is coming from. And they all have the right version of that addon (sf + m4's).
The m4's are really just there to hold us over until we get proper gear, namely FN FAL and G3A3.
Checked and I did, removed them. They should not cause problem though. The weird thing is I haven't placed anything that should load them. The only BAS kit I have is what my soldiers are carrying with them.
Deleted it from the addons folder though, and will re-pbo the mission.
And from what they told me, it crashed when they selected that mission from the missionlist and pressed "ok".