Never heard of that error jbufferstream ... wierd.
Doesn't look like a CB bug. Must be something wierd in your joomla installation
Sometimes live_site is set to something else than '' in joomla 1.5 configuration (in 1.0 it needs to be set, but not in 1.5).
Can you uninstall other components ?
If you installed with ftp installation enabled, you need to uninstall with ftp enabled too. Same the other way around.
If all fails, maybe easiest to do an expert upgrade using FTP to overwrite files, and then a database upgrade, like explained in README.