2 If VBScript

I need some help with my script.

My script should be checking 2 properties

If PropVal is not "Self" the other value (Contact) should be Null or empty.

Option Explicit

Dim szPropertyName, szPropVal
szPropertyName = PropertyDef.Name
szPropVal = PropertyValue.GetValueAsUnlocalizedText


If not szPropVal = "Self" then
Dim szContactVal : szContactVal = PropertyValues.SearchForProperty(1257).TypedValue.DisplayValue

If szContactVal <> "Self" Then
Err.Raise MFScriptCancel, "ContactVal should be empty."

End if
End if

Thank you.