Associate Structure with PDB file does not work

I am trying to associate a sequence with my structure in a PDB file. Clicking on the appropriate menu item does not bring up any dialog. Please help. I am running 2.8.1 on OS X 10.8.5.

Thanks,
Mark

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_________________________________
Mark A. Saper, Ph.D.
Associate Professor of Biological Chemistry, University of Michigan
c/o Biophysics, Chem 3040
930 N University Ave
Ann Arbor MI 48109-1055 U.S.A.
saper@umich.edu phone (734) 764-3353 fax (734) 764-3323