Javascript Not Pulling Value From Form

userName = Global.getComponent('centerRegion').UserName.getValue();

That code pops up with the error

{"browserEvent":"'Global.getComponent(...).UserName' is null or not an object","button":-1,"ctrlKey":false,"xy":[0,0]}

When I run it on this form:

Using Form As New WebControls.Forms.Form
With Form
.ID = "Test"
.ItemName = "connector"
With .Toolbar
.UseDefaultButtons = False
.AddButton(Forms.FormToolbar.ButtonType.Save)
.AddButton(Forms.FormToolbar.ButtonType.Cancel)
.AddButton("Test Connection", "testConnection", "icon-button-testconnection", , "Test")
End With
With .CenterRegion
.Id = "centerRegion"
With .AddFieldSet("Activate Service")......................