Hello again!

I am working on an inventory sort/spread macro, and am trying to make it as user-friendly as possible for my boss, but I'm having a problem with a bit of code. I want the macro to run ONLY if certain Column Headers are present on the worksheet (in this case, "MPN" and "Inventory Number"), and if they are, I want to use those found column headers as Sort Keys. I currently have this:

Formula: copy to clipboard 
    Dim rngMPN As Range

    Set rngMPN = Range("A1:Z1").Find("MPN")

    If rngMPN Is Nothing Then

    MsgBox """MPN"" column was not found."

    Exit Sub

    End If



    Dim rngSKU As Range

    Set rngSKU = Range("A1:Z1").Find("Inventory Number")

    If rngSKU Is Nothing Then

    MsgBox """SKU"" column was not found."

    Exit Sub

    End If



    'This sorts the selected data, first by MPN, then by SKU

    Selection.Sort Key1:=rngMPN.Address, Key2:=rngSKU.Address, Order1:=xlAscending, Header:=xlYes, _

    MatchCase:=False, Orientation:=xlTopToBottom


I'm still rusty on addresses and defining ranges, so I'm sure I don't have the Key1 and Key2 formatting right, as it gives me a "THE FORMULA YOU TYPED HAS AN ERROR" code. Can anyone assist me?