Creating pdf/a1b from pdf problem

I've read a lot about how to do create a pdf/a1b from a pdf.  In Acrobat XI, I've created an Action in the Action Wizard to use Preflight to do this.  I even tried Save As... as a pdf/a1b.  Every time Acrobat gets to "Applying fixups" it freezes and Acrobats says "Not Responding."  Can someone please help with this?

Thanks