LaTeX Warning: Reference `last@page' on page N undefined on input

Hi all,
I use prosper slide presentation like
http://prosper.sourceforge.net/files/slides-cp2000.tex.gz
I use prosper.cls and I have got one error:

LaTeX Warning: Reference `last@page' on page N undefined on input

where N is firstpage<=N<=lastpage of slide presentation.
In each slide I have got p/?? format.

if I remove from prosper.cls evidences about string:

\ifallPages/\realpageref{last@page}\fi

then I have not got this error.
How could I visualize lastpage in each slide with format p/pp without
this error?

With thanks in advance.

Best,

Alessandra Bilardi
=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=
  CRIBI, University of Padova, Italy
    http://genomics.cribi.unipd.it
  http://www.linkedin.com/in/bilardi
=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=

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