velocity issue on pushing an object forward.

I no longer get an error, but the force doesn't take play.

Yes the grenade has a rigidbody, and yes I have tried raising the force. It doesn't move a bit. Is the line of code not good for pushing objects?

You should probably rather try something like this using AddRelativeForce:

 Grenade.rigidbody.AddRelativeForce (Vector3.forward * 10);

Still no luck. Anything I could be missing on the grenade? The rigid body is at its default settings.

Could you post the whole script so I can have a quick look?
Can't see anything wrong with the code, should work fine if the grenade has a rigidbody attached.. Although you will of course want to test some different values to make sure there isn't just too little force.
For example try changing the 10 to a 100 etc:

 Grenade.rigidbody.AddRelativeForce (Vector3.forward * 100);

The force is 1000.

 #pragma strict
 
 var ThrowPower : float = 1000;
 var Grenades : int;
 var $$anonymous$$axNades : int;
 var Grenade : GameObject;
 var ShootTimer : float;
 var cooler : float = 4;
 
 function Start () {
 
 }
 
 function Update () {
     if(ShootTimer > 0) {
         ShootTimer -= Time.deltaTime;
     }
     if(ShootTimer < 0) {
         ShootTimer = 0;
     }
 
     if(Input.Get$$anonymous$$ey($$anonymous$$eyCode.G) && Grenades != 0 && ShootTimer == 0) {
         grenadefunction();
         Grenades = Grenades - 1;
         ShootTimer = cooler;
     }
 
     maximus();
 }
 
 function grenadefunction() {
     Instantiate(Grenade, transform.position, Quaternion.identity);
     Grenade.rigidbody.AddRelativeForce (Vector3.forward * ThrowPower);
 }
 
 function maximus() {
     if(Grenades > $$anonymous$$axNades) {
         Grenades = $$anonymous$$axNades;
     }
 }