postgres=# create table text_test (id int,info text);
CREATE TABLE
postgres=# insert into text_test values (1,E'x00');
ERROR: invalid byte sequence for encoding "UTF8": 0x00

create table test_varchar(id int,name varchar(20));
insert into test_varchar values (1, 'name' + char(0));
insert into test_varchar values (1, 'name' + '');

invalid byte sequence for encoding "UTF8": 0x00

PostgreSQL doesn't support storing NULL (x00) characters in text fields (this is obviously different from the database NULL value, which is fully supported).

If you need to store the NULL character, you must use a bytea field - which should store anything you want, but won't support text operations on it.

Given that PostgreSQL doesn't support it in text values, there's no good way to get it to remove it. You could import your data into bytea and later convert it to text using a special function (in perl or something, maybe?), but it's likely going to be easier to do that in preprocessing before you load it.

Source:http://stackoverflow.com/questions/1347646/postgres-error-on-insert-error-invalid-byte-sequence-for-encoding-utf8-0x0

if (!IS_HIGHBIT_SET(*mbstr))
    {
      if (*mbstr != '')
      {
        mb_len++;
        mbstr++;
        len--;
        continue;
      }
      if (noError)
        return -1;
      report_invalid_encoding(encoding, mbstr, len);
    }

#define IS_HIGHBIT_SET(ch)   ((unsigned char)(ch) & HIGHBIT)
#define HIGHBIT         (0x80)

UPDATE: This seems to work:
 
Select * from TABLE
where UNICODE(SUBSTRING(naughtyField, LEN(naughtyField), 1)) = 0
So:
 
Update TABLE
SET naughtyField = SUBSTRING(naughtyField, 1, LEN(naughtyField) - 1)
where UNICODE(SUBSTRING(naughtyField, LEN(naughtyField), 1)) = 0
Source:http://stackoverflow.com/questions/3533320/sql-server-remove-end-string-character-0-from-data