How do I fix this error?

I am making a 2d Infinite Runner game and was making a script for the spawn pads to generate. I have no idea how to fix the error.

The error: Assets/Scripts/SpawnScript.cs(18,29): error CS0178: Invalid rank specifier: expected ,' or ]'

Also: Assets/Scripts/SpawnScript.cs(23,1): error CS8025: Parsing error

The script is:

 using UnityEngine;
 using System.Collections;
 
 public class SpawnScript : MonoBehaviour {
 
     public GameObject[] obj;
     public float spawnMin = 1f;
     public float spawnMax = 2f;
 
     // Use this for initialization
     void Start () {
         Spawn ();
     
     }
     
     void Spawn ()
     {
         Instantiate(obj[Random.Range 0, obj.GetLength(0))], transform.position, Quaternion.identity);
         Invoke ("Spawn", Random.Range (spawnMin, spawnMax));
     }
     
     }
 }

If anyone could help, that would be awesome. Thanks.