Error message 'The multi-part identifier "SupTr.AcYrPr" could not be bound

I have this error message when making the following statement in a vba project:

     QueryString = "SELECT SUM(SuptTr.Am) " & _
      "FROM " & Eget_firma & ".dbo.SupTr SuptTr, " & 
    Eget_firma & ".dbo开发者_如何学运维.Actor Actor " & _ 
"WHERE Actor.Gr9 = " & Firma_internt & " 
AND SuptTr.SupNo = Actor.SupNo AND SupTr.AcYrPr <= " & RegnPerTil & " "

I've found this to be caused most often by misspelling, or by mistakenly attempting to reference a column in the wrong table. I know I've run into it in other circumstances (i.e., when it's all correctly spelled & attributed), but can't recall now exactly what caused it or what I did about it. I'd be more help if I could....