error in upgrading

[Joep L. Blom]

I have a small annoying problem while upgrading ubuntu hardy.
As I don't want to upgrade to Intrepid, due to the many problems a.o. 
with nvidia (I have an old Geforce video-card) I want to keep hardy updated.
After what problems with installing nspluginwrapper (thanks Noop)flash 
works without a problem in firefox.
However, every time I use the upgrade-manager, it comes back with:
"subprocess /usr/bin/dpkg returned an error code (1)"
It than tries to correct this by again installing flash-plugin-nonfree, 
it saya flas-plugin is installed (true), it then encounters an illegal 
option (-n) and stops, telling me again there is the error -1.
Sorry for the long explanation as it is only 'annoying' but I would like 
to solve it.
system: AMD-64, GEforce 4000 ubuntu hardy kernel 2-6-24-19.
Can anybody give some help how to correct this?
joep