I am running Kubuntu 8.04.1 using KDE 4.1.2. I have this problem on a 64 bit and 32 bit machine.

When I right-click on the desktop, choose "Add widgets", scroll down to "Notes" and drag it onto the desktop, I get an "unknown widget". (That's what it calls it when I delete it.)

Is there someone else who has seen this who could help? Also, is there a configuration file is could look at to see if some setting is wrong?

That sounds more like an incompatible plasmoid file. Does that only happen with the notes plasmoid? Also, make sure you have kdeplasma-addons installed, not extragear-plasma.

neverendingo -- it was the packages. I installed kdeplasma-addons and magically the notes plasmoid works.

Yes, it was only the notes plasmoid that was doing this.

THANK YOU! I didn't use knotes for a long time, but recently really started liking it. Not having that under KDE4 was like missing a limb.

Ok, nice to hear.
Can you please mark this thread as solved? (Edit initial post and add a [SOLVED] to the title). Thanks.