ERROR: cache lookup for userid 26 failed

Greetings,

Does anyone know what is this error?

ERROR: cache lookup for userid 26 failed

Some system tables are inacessible in my database but I can access others. I tried to check pg_tables, but it's blocked :

persona=> select * from pg_tables;
ERROR: cache lookup for userid 26 failed
persona=>

The table pg_class tells me that I'm the user of the table (me, postgres user), but always I get this msg. What can be done to kick it out?

persona=> select * from pg_class
persona-> ;
relname | reltype | relowner | relam | relpages | reltuples | rell
ongrelid | relhasindex | relisshared | relkind | relnatts | relchecks | reltriggers | reluk
eys | relfkeys | relrefs | relhaspkey | relhasrules | relacl
---------------------------------+---------+----------+-------+----------+-----------+-----
---------+-------------+-------------+---------+----------+-----------+-------------+------
----+----------+---------+------------+-------------+--------
pg_type | 71 | 26 | 0 | 2 | 122 |
0 | t | f | r | 16 | 0 | 0 |
0 | 0 | 0 | f | f |
pg_attribute | 75 | 26 | 0 | 6 | 461 |
0 | t | f | r | 15 | 0 | 0 |
0 | 0 | 0 | f | f |
pg_proc | 81 | 26 | 0 | 26 | 1083 |
0 | t | f | r | 16 | 0 | 0 |
0 | 0 | 0 | f | f |

tele_fidel_hierarq | 0 | 26 | 0 | 176 | 6592 |
0 | t | f | r | 7 | 0 | 1 |
0 | 0 | 0 | f | f |
tipo_atendimento | 0 | 26 | 0 | 10 | 1000 |
0 | t | f | r | 3 | 0 | 2 |
0 | 0 | 0 | f | f |
(69 rows)

My linux users are ok. Postgres has 26 as user_id.

[postgres(at)bxsgalena postgres]$ cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
...
postgres:x:26:26:PostgreSQL Server:/home/postgres:/bin/bash

[postgres(at)bxsgalena postgres]$ cat /etc/group
root:x:0:root
...
postgres:x:26:

The database was working very well, but I don't know what was done to it, because another guy did the last maintenance.

That's all for now. Thanks in advance and my best regards!