Check if a drive exists

[DavidGraham167]

I'm using the following code to check if a file has been defined.

If txtGradeObs.Text = "" Or Dir(txtGradeObs.Text) = "" Then
     MsgBox("Specify the Grade job of Obstructions", vbExclamation, MsgBoxTitle)
     Exit Sub
End If

I'm getting an error if the drive does not exist. I don't think this was a problem in VB6.
I'm getting an IO exception - bad file name or number.
How can I get this to work?
Thanks