pg_dump, ERROR: More than one tuple returned

Hey all,

I have a bad problem here which is preventing the backup of my postgres
database.

Here goes:

$ sudo su - postgres
$ pg_dump -x -Ft nvplayer > nvplayer-010920.tar
getDatabase(): SELECT failed.  Explanation from backend: 'ERROR:  More
than one tuple returned by a subselect used as an expression.
'.

Any suggestions?