Sorry for double post , I just want to thank you all for your help. I made it , there's not a problem anymore. 
Here's another screenshot. 
  
Screenshot 
  
// Weapon Stations --------------------------------------------------------- 
  
  
[LeftOuterWingStation] 
SystemType=WEAPON_STATION 
StationID=1 
StationGroupID=1 
StationType=EXTERNAL 
AttachmentPosition=-2.68,-1.49,-0.42 
AttachmentAngles=0.0,0.0,0.0 
LoadLimit=500.0 
LengthLimit=3.5 
AllowedWeaponClass=BOMB,RCKT,RP,IRM,FT,EOGR,ARM,LGB -> I just added "LGB" to AllowedWeaponClass line and now it works! 
AttachmentType=WP,NATO,USAF,USN,ISRAEL,FRANCE 
ModelNodeName=WingPylon_Outer_L 
PylonMass=60 
PylonDragArea=0.02 
LaunchRailNodeName=MissileRail_Outer_L 
LaunchRailHeight=0.10 
LaunchRailMass=25 
FuelTankName=Tank490_MiG21 
  
[RightOuterWingStation] 
SystemType=WEAPON_STATION 
StationID=2 
StationGroupID=1 
StationType=EXTERNAL 
AttachmentPosition=2.68,-1.49,-0.42 
AttachmentAngles=0.0,0.0,0.0 
LoadLimit=500.0 
LengthLimit=3.5 
AllowedWeaponClass=BOMB,RCKT,RP,IRM,FT,EOGR,ARM,LGB 
AttachmentType=WP,NATO,USAF,USN,ISRAEL,FRANCE 
ModelNodeName=WingPylon_Outer_R 
PylonMass=60 
PylonDragArea=0.02 
LaunchRailNodeName=MissileRail_Outer_R 
LaunchRailHeight=0.10 
LaunchRailMass=25 
FuelTankName=Tank490_MiG21