Variable assignment character limit?

Question

I am a developer using PL/SQL. In a procedure, when I try to assign more than 1000 characters to a variable I get "unknown error" I can assign 1000 characters with no problem, 1001 gives the error. I have declared the variable using multiple different data types (varchar2, nvarchar2, etc) and using different lengths (1999, 2000, 4000, 32000). Nothing works. I need to fix this because I need to assign a sql statment to a variable to execute with "execute immediate" and I can't do it because the sql statement is greater than 1000 characters.
Ex:
Sql_stmt varchar2(4000)
sql_stmt := "xxxxxxxx ---> out to 1001 characters"
when this line is executed I get "unknown error"
Could this be a configuration setting of some sort?

Answer 1

What is the full error code that goes with "unknown error"? Oracle errors normally start with SP2, PLS, ORA etc.
Does this work for you in SQL*Plus?
SQL*Plus: Release 11.1.0.6.0 - Production on Wed Sep 22 23:28:15 2010
Copyright (c) 1982, 2007, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
DECLARE
   sql_stmt2 VARCHAR2(2000);
BEGIN
   sql_stmt2 := LPAD('x', 999, 'x');
   sql_stmt2 := LPAD('x', 2000, 'x');
   DBMS_OUTPUT.PUT_LINE('Length of sql_stmt2 = ' || LENGTH(sql_stmt2));
END;
Length of sql_stmt2 = 2000
PL/SQL procedure successfully completed.