Datevalue not working when " / / " appears

[Burt_100]

Hi
I am importing data from an external source which is importing it as text, I have been using the datevalue formula below and it works great in column A however in columns G,J,K I am getting a type mismatch error due to the suspected " / / " appearing when a date is not available, Any ideas how I can get around this?

Sub DateValu()
    For Each cell In Range("Q2:Q3000")
        If Not IsNumeric(cell) Then cell.Value = DateValue(cell)
    Next cell
End Sub