Hello
I'm using kubuntu 8.04. I've been following the instructions found in an ubuntu forum for setting up multimedia apps and mplayer plugin. I received the following errors when executing the final step to write to mplayerplug-in.conf

dan@dan:~$ sudo kwrite $HOME/.mplayer/mplayerplug-in.conf
[sudo] password for dan:
Error: "/var/tmp/kdecache-dan" is owned by uid 1000 instead of uid 0.
Error: "/tmp/kde-dan" is owned by uid 1000 instead of uid 0.
Error: "/tmp/ksocket-dan" is owned by uid 1000 instead of uid 0.

The mplayer plugin doesn't work in firefox. However the mplayerplug-in.conf file does exist and I successfully wrote to it as the post instructed

The file is in your home directory so it is owned by you. In other words, sudo is not required in this case - in fact, it may results in certain user files being given administrator level permissions, potentially causing applications to fail when run by regular users. This is just a guess but I think that is what the errors you posted are all about: those files are owned by you (UID1000) but sudo tried to promote them to root (UID 0). Have a look at the permissions on your mplayer directory and its contents.

the permissions on ./mplayer are "dan" not root. Can I expect problems? The mplayer plugin is now working in firefox

I don't expect any issues, no. Have you also checked the permission on the conf file inside .mplayer? That's the one that may have been given root permissions. It won't hurt but it will make it less convenient to edit.