Client-site "lo_export"

Hello!

I use client-side "lo_export" for save large object to file. If i login
as database owner then i do not have error (output file exists), but if
i login as not database owner then function "lo_export" returning -1. My
code is simple:

PGresult *res = PQexec(pg_conn, "begin");

PQclear(res);

int ret = lo_export(pg_conn, repo_oid, filename);

res = PQexec(pg_conn, "end");

PQclear(res);

OS: Win7, 32-bit
PostgreSQL: 9.1.0

What could be the problem?

Thank you for helping!