Edit the install_dir/pointbase/tools/serveroption/pbenv.conf configuration file, changing the line:
PB_JAVA=%%%PB_JAVA%%%
to
PB_JAVA=J2SE_location
where J2SE_location is the directory where the J2SE is installed. If you installed J2SE with Application Server, it is installed by default to install_dir/jdk. After making this change, you can start PointBase using the startserver script.