Huh? Mysterious Function Error

Tom, Stephan, Jan, Etc.
Can you help me with this one?  I can't figure out what is meant by
this error message:

I have a long, complicated PL/pgSQL function called
fn_modify_candidates(INT4,INT4,INT4).

When I call:
SELECT fn_modify_candidate(1004,5,278417036)

I get:
ERROR:  unexpected SELECT query in exec_stmt_execsql()

Help?
                -Josh Berkus

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