Game crashing v1.2.8

So basically, me and a friend of mine are playing together on my server for about 40~50 min, when all of a sudden after killing a magma worm too quicly (wich i guess was the cause of it) her game crashes with this error:
___________________________________________
############################################################################################
FATAL ERROR in
action number 1
of Step Event2
for object oWormHead:

Unable to find any instance for object index '249812'
at gml_Object_oWormHead_Step_2
############################################################################################
It's already the 5th time or so and i would like to know if there's a fix to this, been searching google and the forum for some time already and got nothing..