Comment 3 for bug 61421

Same here.

I edited the postinst script, adding a "set -x" to it. Heres the relevant output:

+ return 0
+ '[' -x /etc/init.d/flashplugin-nonfree ']'
+ update-rc.d flashplugin-nonfree multiuser
usage: update-rc.d [-n] [-f] <basename> remove
       update-rc.d [-n] <basename> defaults [NN | sNN kNN]
       update-rc.d [-n] <basename> start|stop NN runlvl [runlvl] [...] .
                -n: not really
                -f: force
dpkg: error processing flashplugin-nonfree (--configure):

"multiuser" is related with an update to update-rc.d as described in https://wiki.ubuntu.com/Teardown. But this update will only be availiable in ubuntu 6.10 or throw a backport to dapper.

My 2cents: IFF this package is a backport, than it would better explicitly depend on a backported update-rc.d version.