You are right. There is an error in the code. Try replacing the If Then Else that is just previous to the code you posted here. This code will exit the sub and skip the code you posted. See if this works...
Code:
If Not IsNull(Me.cmbPO) Then
strPO = Me.cmbPO.Column(1)
lngUnits = Me.cmbPO.Column(2)
strMsg = strMsg + " " & vbCrLf
strMsg = strMsg + "PO # " & strPO & " has " & vbCrLf
strMsg = strMsg & lngUnits & " units remaining in inventory. "
If Not IsNull(Me.cmbCont) Then
lngBOL = Me.cmbCont.Column(1)
lngUnits = Me.cmbCont.Column(2)
strMsg = strMsg + " " & vbCrLf
strMsg = strMsg + "Bill of Lading # " & lngBOL & " has " & vbCrLf
strMsg = strMsg & lngUnits & " units remaining in inventory. "
End If
MsgBox strMsg, vbInformation, "Here is your answer."
Exit Sub
End If