Oracle Developer 6i forms and reports client unable to connect with oracle database 11g r2 64 bits by default

Oracle developer 6i wasn't able to connect at (11.2.0.1) oracle database with default multi-byte CHARACTER SET "AL32UTF8" .
altering the single-byte CHARACTER SET as "WE8MSWIN1252" then developer able to connected.

(From some pc's developer 6i builder just flash out (close) 
and from another pc its says form designer need to close because of  unable to run .)

Info:- 
oracle database version
---------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
PL/SQL Release 11.2.0.1.0 - Production
CORE    11.2.0.1.0    Production
TNS for 64-bit Windows: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

OS is :- Windows enterprize server 2008 R2




Developer forms builder 6i.
 
Below are the steps to alter the CHARACTER SET.
(first test it at testing server)

SQL> shutdown immediate
SQL> startup mount
SQL> alter system enable restricted session;
SQL> alter system set job_queue_processes=0;
SQL> alter system set aq_tm_processes=0;
SQL> alter database open;

SQL> ALTER DATABASE CHARACTER SET WE8MSWIN1252;
SQL> shutdown immediate
SQL> startup


To see the value of CHARACTER SET

SELECT value$ FROM sys.props$ WHERE name = 'NLS_CHARACTERSET' ;



or

SELECT * FROM NLS_DATABASE_PARAMETERS;

[Note :- 

"ALTER DATABASE CHARACTER SET INTERNAL_USE WE8MSWIN1252" 

It strongly recommend that you not use the INTERNAL_USE clause unless Oracle support explicitly tells you to do so. As the name implies, INTERNAL_USE is not properly documented and is not designed to be used by customers in the field.

To change the NLS_CHARACTERSET or NLS_NCHAR_CHARACTERSET by updating props$ . This is NOT supported and WILL corrupt your database. This is one of the best way's to destroy a complete dataset. Oracle Support will TRY to help you out of this but Oracle will NOT warrant that the data can be recoverd or recovered data is correct. Most likely you WILL be asked to do a FULL export and a COMPLETE rebuild of the database.