test:clone_structure problems with Postgres

(in C:/projects/books/TheatreTickets)

** Invoke db:test:clone_structure (first_time)

** Invoke db:structure:dump (first_time)

** Invoke environment (first_time)

** Execute environment

** Execute db:structure:dump

** Invoke db:test:purge (first_time)

** Invoke environment

** Execute db:test:purge

** Execute db:test:clone_structure

psql:db/development_structure.sql:15: ERROR: language "plpgsql"
already exists

This doesn't seem to be a common configuration problem. I did try
"dropping: the language on the command line, but no help.
any ideas would be appreciated...