Missing Earth Distance Functions Under Debian

Hi All. I was wondering whether someone could help me explain a weird
PostgreSQL error I've encountered.

I have two machines running Debian Sarge stable, the first has been
operating as a
database server for some time and the other I have just set up identically
to run as a backup database. Both machines used the default database setup
option during installation.

Some of my scripts rely on the earth distance functions contained in the
'postgresql-contrib' package, but for some reason the backup PostgreSQL
database does not recognise these functions. Eg. my latitude/longitude to
distance converter, which runs fine on the main machine, generates this
error message:

"ERROR: function ll_to_earth(numeric, numeric) does not exist
HINT: No function matches the given name and argument types. You may need
to add explicit type casts."

I've tried reinstalling the package in question but it had no effect. Does
anyone have a theory why it would run on one and not the other and/or how I
can get the earth distance functions working?

Regards,

-Duncan