Hi guyz. The modelspecial problem occures when there is a problem in the config.cpp. When you are typing the magazine and weapon load out for the soldiers and put 2 commas ("catm16",,"catm16","catm16".) This basically means that the game can not recognize the weapon or magazine and so to not crash the game the game instead gives this error message. This also happens when you do not have the weapons the addon requires. For the HK pack 2. You will need the "UPDATED" M4A1 pack which also includes the desert camo version of the M4A1.
Hope it helped.