character set problems

You just installed Oracle Database XE version (10g or 11g) and try to connect with forms 6i. When you put the connection string and hit ENTER to connect then Forms/Reports builder hang and "Forcefully Closed".

What happen ?

It's just about the CHARACTER SET mismatch.  Typically XE database version most surelly 
11g XE use Unicode CHARACTER SET, which is "AL32UTF8".

Forms/Reports 6i doesn't support this and supports ("UTF8","WE8MSWIN1252")

Moreover,

Oracle Database 11g Express Edition has no provisions to change/use other charactersets than AL32UTF8 as NLS_CHARACTERSET and AL16UTF16 as NLS_NCHAR_CHARACTERSET
The NLS_CHARACTERSET is used for CHAR, VARCHAR2, LONG and CLOB columns;
The NLS_NCHAR_CHARACTERSET is used for NCHAR, NVARCHAR2 and NCLOB columns.

So, if you migrate data from any previous version of Database like 10g with special character, you will see the bellow problem when importing. 

SQL> create table t( c varchar2(3) );

SQL> insert into t values( 'abç' );
insert into t values( 'abç' )
*
ERROR at line 1:
ORA-12899: value too large for column "SCH"."T"."C" (actual: 4, maximum: 3)


What to do ?
Simply alter the CHARACTER SET to previously supported one.

[Script]

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\Windows\system32>CD C:\oraclexe\app\oracle\product\11.2.0\server\bin

C:\oraclexe\app\oracle\product\11.2.0\server\bin>SET ORACLE_HOME=C:\oraclexe\app
\oracle\product\11.2.0\server

C:\oraclexe\app\oracle\product\11.2.0\server\bin>SET ORACLE_SID=XE

C:\oraclexe\app\oracle\product\11.2.0\server\bin>echo %ORACLE_SID%
XE

C:\oraclexe\app\oracle\product\11.2.0\server\bin>SQLPLUS/NOLOG

SQL*Plus: Release 11.2.0.2.0 Production on Fri May 23 19:53:42 2014

Copyright (c) 1982, 2010, Oracle.  All rights reserved.

SQL> CONN SYS/SYSTEM11g AS SYSDBA
Connected.
SQL> SHUTDOWN IMMEDIATE
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL>
SQL>
SQL>
SQL> STARTUP RESTRICT
ORACLE instance started.

Total System Global Area  535662592 bytes
Fixed Size                  1384760 bytes
Variable Size             272633544 bytes
Database Buffers          255852544 bytes
Redo Buffers                5791744 bytes
Database mounted.
Database opened.
SQL>
SQL>
SQL> ALTER DATABASE CHARACTER SET INTERNAL_USE WE8MSWIN1252;

Database altered.

SQL>
SQL>
SQL> SHUTDOWN IMMEDIATE
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL>
SQL>
SQL> STARTUP
ORACLE instance started.

Total System Global Area  535662592 bytes
Fixed Size                  1384760 bytes
Variable Size             272633544 bytes
Database Buffers          255852544 bytes
Redo Buffers                5791744 bytes
Database mounted.
Database opened.
SQL>SQL> select * from v$nls_parameters where parameter like '%CHARACTERSET%';

PARAMETER
----------------------------------------------------------------
VALUE
----------------------------------------------------------------
NLS_CHARACTERSET
WE8MSWIN1252

NLS_NCHAR_CHARACTERSET
AL16UTF16