Argument Exception: "An item with the same key has already b

Well, all the keys of a Dictionary must be unique - hence the error.

You can avoid the error by checking first whether the key already exists, like this:

private void UpdateProduct( List account, string userEmail, List products )

{

Dictionary productUpdateDictionary = new Dictionary();

for ( int i = 0; i < products.Count; i++ )

{

if(!productUpdateDictionary.ContainsKey(products[i].code))

{

productUpdateDictionary.Add( products[i].code, new ProductUpdate { Index = i, ProductCode = products[i].code } );

}

}

However, this may not be entirely satisfactory and a different approach would be to modify products[i].code in some way so that it differs from the previous key and can therefore be added to the Dictionary.