I recently upgraded from ubuntu karmic to lucid which is an LTS.

Kdenlive was working perfectly in karmic. Now there is no preview window.

I get this error:

Could not create the video preview window.
There is something wrong with your Kdenlive install or your driver settings, please fix it.

What should i do?

I don't know. It works for me, and all I can say is that this is not a known problem (first I heard of it). Try reinstalling mlt and kdenlive.

what's your preference set to for video playback? i believe mine is set to x11 (i think anyway) maybe you could check that. audio is set to pulseaudio. i am using lucid also and i don't have a problem. isn't the playback settings also controlling the preview window? good luck.

I get playback with X11, but the playback window is transparent which is useless. Any way to set it to not be transparent?

Okay I solved it. Had to turn off compiz (with compiz fusion icon) and use metacity as the window decorator. :)