I am surprised this one hasn’t been fixed as I can see on google mentions of this back to 2007.
Anyway many google results tell you to execute this command.
gconftool-2 --install-schema-file /usr/etc/gconf/schemas/guake.schemas
This also gives a file not found error. I did a quick updatedb and locate guake.schemas. Here is an updated command for Ubuntu 10.10 to fix the “guake.schemas gconf schema isn’t installed” error message.
gconftool-2 --install-schema-file /usr/share/gconf/schemas/guake.schemas
For command line novices: To fix this load up a terminal, execute sudo su and enter your password then copy and paste the above command in.