Problem with "z_" in Unicode-DB

Hi,

i have following problem:

I created a database with encoding UNICODE

CREATE DATABASE elements
  WITH ENCODING = 'UNICODE';


In this db there is a table "tblassets"

CREATE TABLE public.tblassets
(
  id serial NOT NULL,
  uri text NOT NULL,
  CONSTRAINT tblassets_pkey PRIMARY KEY (id)
) WITHOUT OIDS;


When i try to execute this select, i get an error:

Statement:
SELECT ID FROM tblAssets WHERE uri like
'/files/AssetStore/postgreSqlTest/ratz_ruebe.jpg' ;

Error:
ERROR:  Invalid UNICODE character sequence found (0xc000)


If I try this, there is no error:

SELECT ID FROM tblAssets WHERE uri like
'/files/AssetStore/postgreSqlTest/ratzruebe.jpg' ;
SELECT ID FROM tblAssets WHERE uri like
'/files/AssetStore/postgreSqlTest/raty_ruebe.jpg' ;

Has PostgreSQL a problem with the characters "z_"?

Platform is:
Redhat 8.0 (english)
PostgreSQL 7.3.3 (redhat binaries)
Client pgAdmin3

Regards, Daniel