This is my error I think it effects the lines

guitex.pixelInset.x = Screen.width - achievementTex.width - edgeMargin;

guitex.pixelInset.x = Screen.width - achievementTex.width - edgeMargin;

Operator '-' cannot be used with a left hand side of type 'int' and a right hand side of type 'Object'.

pragma strict

 var firstStepTex:Texture;
 
 private var firstStepTaken:boolean;
 private var edgeMargin;
 
 function Start(){
     edgeMargin = Screen.width * .01;
 }
 
 function playerMoved(){
     if(!firstStepTaken){
         unlockAchievement(firstStepTex);
         firstStepTaken = true;
     }
 }
 
 function unlockAchievement(achievementTex:Texture){
     var go:GameObject = new GameObject("Achievement Object");
     go.transform.position = Vector3(0,0,0);
     go.transform.localScale = Vector3(0,0,0);
     var guitex:GUITexture = go.AddComponent(GUITexture) as GUITexture;
     guitex.texture = achievementTex;
     guitex.pixelInset.width = achievementTex.width;
     guitex.pixelInset.height = achievementTex.height;
     guitex.pixelInset.x = Screen.width - achievementTex.width - edgeMargin;
             guitex.pixelInset.x = Screen.width - achievementTex.width - edgeMargin;
 }