The natbib package in LATEX checks to see whether the
chapter command is defined. If so it decides to use that for
the bibliography headings. This will generally place the bibliography
on a new page, which is what you would expect for a book. However,
the llncsLATEX document class does define the
chapter command, but is used generally for writing articles! A
simple solution is to tell natbib to use section
rather than chapter for the bibliography: