Plasma doesn't start

When I log in to the KDE session, I see the progress bar with the icons appearing from a blur and hear a music.
Then I observe the black screen and the mouse pointer, nothing else.
If I press Alt-F2, I can see the program launch dialog.
If I enter 'plasma' in it, then the taskbar and the desktop wallpaper, and other plasmoids appear.

The file ~/.xsession-errors contains the following lines, related to plasma:

klauncher(17532) KConfigGroup::readXdgListEntry: List entry Categories in "/usr/share/applications/screensavers/plasma.desktop" is not compliant with XDG standard (missing trailing semicolon).
kdeinit4: preparing to launch /usr/bin/plasma
<unknown program name>(17638)/ checkComposite: Plasma has an argb visual 0x91f99b0 23068673
<unknown program name>(17638)/ checkComposite: Plasma can use COMPOSITE for effects on 0x91f2128
plasma: Unknown option 'r'.
plasma: Use --help to get a list of available command line options.

I've searched for plasma in this file, it contains some more occurances, but all of them are "plasma" in quotes and issued by the nepomuk.

Then, I've found that file, /usr/share/applications/screensavers/plasma.desktop, it contained the call /usr/bin/plasma -r.
This file has come from the package rss-glx, which has provided the OpenGL screensaver plasma.

I have removed this package and removed ~/.plasmarc and ~/.plasmaappletsrc (? doubts about the latter name) - didn't help.

I use Ubuntu 8.10 with the latest updates.