My desktop effects are suddenly erratic

11.2, Kernel, Gnome 2.28.0

For several months I have had desktop effects enabled, using the desktop cube with 3 desktop columns and working flawlessly. Within the last week the desktop effects spontaneously become disabled. Example: I was reading a web page a few minutes ago, the screen flickered, desktop effects were disabled, the workspace switcher showed four spaces instead of three and no cube.

When I try to re-enable desktop effects (using control center/desktop effects which launches Simple CompizConfig Settings Manager) I get a screen flicker and the Enabled check box remains ticked but none of the settings take effect. Something seems to be overriding the Simple CompizConfig Settings Manager settings. Rebooting fixes things, but only until the next spontaneous reset.

I’ve installed/uninstalled some rpm’s recently trying to fix a sound problem so I imagine that’s how i borked things up. I’m looking for suggestions on how to restore my desktop settings or disable what might be triggering the resets.

Thanks in advance