LukeyBoy is right and I would like to expand on what
he said. When sending information via a web server the
server has to know what kind of content is being
sent and verifies that the outgoing content has the correct
header on it. In the case of static .htm(l) it adds the correct
header for you since it has the correct mime mapping and
the content is not being processed by a forgein handler.
So adding the line that LukeyBoy specified tells apache
that the content is HTML and
should solve your Internal Server Error problem.