Diagram data lost after copying diagrams in powerpoint

[peter]

I run powerpoint 2002 on XP System.
If I create diagrams and copy them to
a different page or even the same page,
the diagram content will not anymore be
available for editing (if one clicks on the
diagram, the numbers in the table, the format
options etc. are lost and an empty space is shown)
Even in copying the whole page of the presentation
one will loose these information.

Have already installed service pack 2, but does not
cure the problem.

Please advise

Thanks,

Peter