VB.NET For loop not running properly

I have been debugging my for loop and I have found that it does not progress through the code it gets to a certain line runs the line comes back to that line once its run and runs it again therefore causing the following error.

Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index

Here's my for loop:

For Each user As Data.DataRow In userData.Rows
    If user Is Nothing Then
        Exit For
    End If
    memberList(userId) = New clsMember(user("UserID"), user("Firstname"), user("Secondname"), user("Username"), user("Password"), user("Email"), user("Rights"))
    userId += 1
Next

The line it gets stuck on is the following:

memberList(userId) = New clsMember(user("UserID"), user("Firstname"), user("Secondname"), user("Username"), user("Password"), user("Email"), user("Rights"))

Whilst debugging I found it runs the first time perfectly comes back around to the for loop tries to run it again without getting to the next line:

userId += 1

And causes the error, I have no idea at all why it is doing this.
If you need any more code I will be happy to provide it.

When adding items to a list (assuming it's not yet populated), you can't just pick the index you'd like the item to occupy and assign it a value. The list needs to have a placeholder there first.

The simplest thing to do is just use List.Add() to add items to your list:

For Each user As Data.DataRow In userData.Rows
    memberList.Add(New clsMember(user("UserID"), 
                                 user("Firstname"),
                                 user("Secondname"), 
                                 user("Username"), 
                                 user("Password"), 
                                 user("Email"), 
                                 user("Rights"))
Next