Plasma Pistol(Mongose error)

Sorry for bad english i'm spanish XD.
There is a problem on having used plasma pistol in the mongose.Here is:
ERROR in
action number 5
of Step Event
for object objMongooseTorso:

Error in code at line 36:
case sprPlasmaPistolCharging:{sprite_index2=sprPlasmaPistolCharging_Layer} break;

at position 46: Unknown variable sprPlasmaPistolCharging_Layer
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Sorry for bad english