you have a couple problems going on here.
1) At line 44 you are setting the $user variable to the value of the $_SESSION['userRole'] variable.
the error is saying that the $_SESSION['userRole'] variable does not exist. there is no where in the code that you are setting the userRole session variable.
2) The code to redirect the user based on user level needs to be applied to the login success page, not the login page.
3) you need to set the getCustomers recordset to filter the username
column on the $_SESSION['MM_Username'] value set by the login.
Then you can set the $_SESSION['userRole'] to use the value from the recordset.