I have a similar problem. I'm using KDE 3.5.2 and FC5
In previous versions of fedora, pressing the volume buttons in kde would result in the audio volume changing, and a progress bar appearing to tell me about it. Now, the volume doesn't change and I get a grey box with the message "It seems that KMix is not running", even though KMix is running! If I quit KMix, then pressing the buttons will cause KMix to actually start, and then the same message pops up telling me that KMix is not running.
So now there are 2 questions:
(1) Is there some way to fix this and get the volume buttons to work with KMix?
(2) If not, the next best option would be to disable these hotkeys and reasign them to something else, like the sound mixer panel applet, but I can't find a simple way to uncouple these keys from kmix. The last reply suggested to remove kmilo: could anyone tell me what kmilo is supposed to do before I remove it and find even more problems?