This is most commonly caused by an addon you have added, its either clashing with something or you have
missed something out. Also have you got the game patched up to date? this is obviously saying you have an
error somewhere with the hmmvw tow! so have you added any humveys? maybe the ExA pack? or the NXZ
humveys? take out the mods or all your mods and start the game in Vanilla, then put the mods in one by one
and then find the one which is causing the error.
If your still not sure on how to add/install addons, then check out this thread