Error when trying to get the userid from AD

Hi everyone,
I got "Reference to a non-shared memeber require an object reference" error message when I used the following code to only get the UserId from AD.  
The error is related to User Would someone please help me look into this to see what is wrong here.  Thank you very much!

Dim vUserID1 As String = User.Identity.Name
Dim vUserID2 As String = vUserID1.Remove(0, vUserID1.LastIndexOf("\"c) + 1)
lblUserID.Text = vUserID2