Excel Macro suddenly starts giving incorrect ActiveCell Data

[simora]

I've had a macro running for over 3 years, but now it has suddenly started returning the incorrect column Number, even when the cursor is firmly in Column 1.

It keeps selecting column Y. EVERY TIME !
It doesn't matter what I select as the ActiveCell.
Any ideas what could be causing this ?
If a virus is a possibility, any suggestions as to where I should start looking.

Here's the code bit that I'm using which is causing the problem.

I added the MsgBox ActiveCell.Column at the end so that I could see what column it was selecting.

Sub GetCell()    
    Dim myRow As Long
    Dim val As String    
    val = ActiveCell.Value
    myRow = ActiveCell.Row    
    If ActiveCell.Column <> 1 Then
        MsgBox ActiveCell.Column
        MsgBox " Select a Lot Number "
        Exit Sub
    End If
    MsgBox ActiveCell.Column
End Sub