Jerome, this has been a known problem for quite some time. Modders are very capable of adding secondary weapons to any unit EXCEPT those with spears. If the spear unit does not have phalanx, if it attempts to use its secondary weapon there is a CTD, without fail.

This appears to be a bug in the animation set. If a unit is given a javelin as a primary and a spear as secondary, no CTD. However, if the spear is primary and the unit is not a phalanx, it will crash, every time.