StartCoroutine and IEnumerator's - Multiple usage of function

Hi guys,

I am trying to build a database using PHP as the database and C# in Unity. I am running into a problem using the StartCoroutine() function on my IEnumerator function.

Here is my code snip-it of the areas I am having trouble:

 public class GUIShopMenus : MonoBehaviour {
     void OnGUI (){
         if (checkPurchase) {
             GUI.BeginGroup( new Rect(Screen.width/2 - 100, Screen.height/2 - 50, 200, 100));
                 GUI.Box( new Rect(0,0,200,100), "");
                 GUI.Label( new Rect(45,10,110,60), "Are you sure you?");
                 
                 if (GUI.Button( new Rect(20,60,70,30), "Yes")) {
                     StartCoroutine(Database_Controller.PurchaseAttemptDatabase(Player_Controller.Character.GetUser(), item, itemType));

and the Database_Controller.PurchaseAttemptDatabase() function:

 static public IEnumerator PurchaseAttemptDatabase (string user, int item, int itemType)
     {
         string accessKey = Md5Sum(user + secretKey);
         string updateKey = Md5Sum(item + itemType + secretKey);
  
         string post_url = database + "accessKey=" + accessKey + "&user=" + WWW.EscapeURL(user) + 
             "&function=purchaseItemAttempt" + "&updateKey=" + updateKey + "&item=" + item + "&itemType=" + itemType;
  
         // Post the URL to the site and create a download object to get the result.
         WWW hs_post = new WWW(post_url);
         yield return hs_post; // Wait until the download is done
 
         if (hs_post.error != null)
         {
             Debug.Log("There was an error purchasing this item: " + hs_post.error);
         } else {
             if (hs_post.text.Length != 0) {
                 if (IsReturnCharacterInfo(hs_post.text)) {
                     string characterInfo = GetInfoFromReturn(hs_post.text);
                     SetPlayerController(characterInfo, user);
                     
                     //For testing
                     Debug.Log(Player_Controller.Character.PrintInfo());
                 } else {
                     Debug.Log(hs_post.text);
                 }
             } else {
                 Debug.Log("Not enough coins!");
             }
         }
     }

What I am trying to do is use the function Database_Controller.PurchaseAttemptDatabase() each time I want to add a new item that the use has to the database.

EDIT: I am calling the Database_Controller.PurchaseAttemptDatabase() function each time the user clicks a button, and I am passing it different parameters for each button that is clicked. But it only seems to work the first time, on the first button click. After that, nothing happens on the other button clicks.

E.G: Both use the OnGUI function above, but may pass different parameters like this:

Button One -> StartCoroutine(Database_Controller.PurchaseAttemptDatabase(user = "Bob", item = 12, itemType = 1))

Button Two -> StartCoroutine(Database_Controller.PurchaseAttemptDatabase(user = "Bob", item = 34, itemType = 4))

Is there anyway I can do this?

Any help would be much appreciated, Thanks! :)