pg_dump: SQL command failed
There are various ways to set the search_path in PostgreSQL.

To diagnose, log into the same database as the same superuser and check:

SHOW search_path;


If it contains dbms_sql, then check your postgresql.conf, databse and role settings to find where it came from.

Use any editor or for instance grep on in a Linux shell to audit postgresql.conf:

grep 'search_path' /your/path/to/postgresql.conf


To check on database and role settings, use the default command line client psql or a graphical GUI like pgAdmin.

In pgAdmin you just select the object in the object browser to see all settings in the SQL pane.

In psql, use

\drds superuser


to see settings for this role. And

\drds '' db_name


to see settings for the database. Or just

\drds 


to see all settings for all roles and databases.