InvalidCastException error and logic error

Hi everyone! Project: i have 6 main objects (6 parents and 6 children) and every time my game starts they take random textures. See below a part of my js code:

 function Start () {
 var texturesCollection: Object[] = Resources.LoadAll("Front_Face_cards");
 var length_ = texturesCollection.length -2;
 var range_1 = Random.Range(0,length_);
 
 var bckgndTxtr_Collection: Object[] = Resources.LoadAll("Back_Face_cards");
 var bckgndTxtr_length_ = bckgndTxtr_Collection.length;
 var bckgndTxtr_range_ = Random.Range(0,bckgndTxtr_length_);

 //all objects (plane objects) get a texture 
         GameObject.Find("card_1").renderer.material.mainTexture = bckgndTxtr_Collection[bckgndTxtr_range_]; //<- here is the error (line 14)
         GameObject.Find("card_2").renderer.material.mainTexture = bckgndTxtr_Collection[bckgndTxtr_range_];
         GameObject.Find("card_3").renderer.material.mainTexture = bckgndTxtr_Collection[bckgndTxtr_range_];
         GameObject.Find("card_4").renderer.material.mainTexture = bckgndTxtr_Collection[bckgndTxtr_range_];
         GameObject.Find("card_5").renderer.material.mainTexture = bckgndTxtr_Collection[bckgndTxtr_range_];
         GameObject.Find("card_6").renderer.material.mainTexture = bckgndTxtr_Collection[bckgndTxtr_range_];
 
 //all objects (plane objects) get a texture, but the following plane objects are children to the ones above, for example "front_card_1" is a child to "card_1" etc.
 if(GameObject.Find("front_card_1") && GameObject.Find("front_card_2")){
     GameObject.Find("front_card_1").renderer.material.mainTexture = texturesCollection[range_1]; //<- here is the error (line 24)
     GameObject.Find("front_card_2").renderer.material.mainTexture = texturesCollection[range_1];
 }
 
 if(GameObject.Find("front_card_3") && GameObject.Find("front_card_6") ){
     GameObject.Find("front_card_3").renderer.material.mainTexture = texturesCollection[range_1+1];
     GameObject.Find("front_card_6").renderer.material.mainTexture = texturesCollection[range_1+1];
 }
 
 if(GameObject.Find("front_card_4") && GameObject.Find("front_card_5") ){
     GameObject.Find("front_card_4").renderer.material.mainTexture = texturesCollection[range_1+2];
     GameObject.Find("front_card_5").renderer.material.mainTexture = texturesCollection[range_1+2];
 }
 }

Problem: the thing is every time i play the scene sometimes i get this compile error saying: "InvalidCastException: Cannot cast from source type to destination type. StartUp.Start () (at Assets/Lvl1/StartUp.js:23)" and sometimes i get this one saying: "InvalidCastException: Cannot cast from source type to destination type. StartUp.Start () (at Assets/Lvl1/StartUp.js:14)" and some other times i don't get any error, which means that the scene works like a charm.

I ask for two things: 1)I don't understand the two above errors. 2)Do i have any other option to shrink somehow the above code, and more specifically, can i type a single line or two instead of the 6 lines i dedicate for my 6 card objects which they get the same texture?

Any help would be most welcome. Thank you in advance!