error with participants when using pgsql

I have errors:
1) message from user 1 to user 11
PDOException: SQLSTATE[22P02]: Invalid text representation: 7 ERROR: invalid input syntax for integer: "user_11" LINE 4: WHERE (base.uid IN ('user_11')) ^: SELECT base.uid AS uid, base.name AS name, base.pass AS pass, base.mail AS mail, base.theme AS theme, base.signature AS signature, base.signature_format AS signature_format, base.created AS created, base.access AS access, base.login AS login, base.status AS status, base.timezone AS timezone, base.language AS language, base.picture AS picture, base.init AS init, base.data AS data, base.push_pass AS push_pass FROM {users} base WHERE (base.uid IN (:db_condition_placeholder_0)) ; Array ( [:db_condition_placeholder_0] => user_11 ) in DrupalDefaultEntityController->load() (line 197 of /home/hwg/src/www/includes/entity.inc).

2) message from user 1 to user 1
PDOException: SQLSTATE[22P02]: Invalid text representation: 7 ERROR: invalid input syntax for integer: "" LINE 4: WHERE (base.uid IN ('')) ^: SELECT base.uid AS uid, base.name AS name, base.pass AS pass, base.mail AS mail, base.theme AS theme, base.signature AS signature, base.signature_format AS signature_format, base.created AS created, base.access AS access, base.login AS login, base.status AS status, base.timezone AS timezone, base.language AS language, base.picture AS picture, base.init AS init, base.data AS data, base.push_pass AS push_pass FROM {users} base WHERE (base.uid IN (:db_condition_placeholder_0)) ; Array ( [:db_condition_placeholder_0] => ) in DrupalDefaultEntityController->load() (line 197 of /home/hwg/src/www/includes/entity.inc).