Had you rebooted the device after installing ASUI? Maybe it didn't properly start and the reboot fixed it, and not the CSSU. But the CSSU is probably good to have installed since it patches various userland apps.
Did you have advanced-power installed on the n800?
It seems the battery applet is mandatory and advanced-power probably disabled that. I will have ASUI do the same in next release, in the mean time you can run (code) as root so you can remove the default battery applet.