Error when retrieving oracle clobs

Question

Here's the sql statement that we are running:
SELECT dbms_lob.substr(sql_statement,dbms_lob.getlength(sql_statement),1) sql_statement FROM query
WHERE query_tk = [Param.1]
If the sql_statement is > 4000 chars, we are getting this error:
Fatal Error
A SQL Error has occurred on query, ORA-06502: PL/SQL: numeric or value error: character string buffer too small ORA-06512: at line 1 .

Answer 1

We are seeing this outside of xmii as well. 
Here's the background.  We originally tried to do a normal insert to the clob (thru xmii) but we got errors when inserting values of more than 4000 chars.  So, we inserted the clob differently (code used below).  That's when we started getting this new error.  Is there another way to insert/retrieve clobs?
   --INSERT "base" row if it does not already exist.
   BEGIN
     SELECT  query_tk
       INTO  v_dummy
       FROM  query
       WHERE query_tk = p_query_tk;
     EXCEPTION
       WHEN NO_DATA_FOUND THEN
         INSERT INTO query
           (query_tk
           ,last_updated_timestamp
           ,sql_statement
         VALUES
           (p_query_tk
           ,SYSDATE
           ,'DUMMY');
   END;
   --Initialize buffer with data to be inserted
   v_copy_length := LENGTH(p_sql_statement);
   -- get LOB handle
   SELECT  sql_statement
     INTO  v_lobloc
     FROM  query
     WHERE query_tk = p_query_tk
     FOR UPDATE;
   dbms_lob.write(v_lobloc,v_copy_length,1,p_sql_statement);