PLpgSQL Stat Problem

I got the following error after trying to copy the example at:

http://www.postgresql.org/mhonarc/pgsql-sql/1999-04/msg00076.html

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test=> select a(pin,first_name) from ibs_subscriber ;
ERROR:  stat failed on file ${exec_prefix}/lib/plpgsql.so
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The file plpgsql.so does exist in /usr/local/pgsql/lib.

Any ideas?

Andy