GetUsersInRole METHOD USAGE

I am trying to use the GetUsersInRole method without success, I get the following error message in my browser: "Index was outside the bounds of array."

The code below is what I wrote:
Dim strUsers(100) As String
strUsers = Roles.GetUsersInRole(txtRolName.Text)

 I also saw the following code and tried it:
Dim strUsers As String()
strUsers = Roles. ...