Answer

To resolve this problem you must identify what the character set is on your client, on your server, and if these character sets are compatible:

1. The character set on an Oracle client is stored in the following key:
   
HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\HOME0\NLS_LANG

   Note: There may be other HOME<N> Registry branches as well. The Oracle client character set is the last section of the value.
   
   For example: If the registry value is: AMERICAN_AMERICA.WE8ISO8859P1 then the character set is WE8ISO8859P1.
2. To determine what character set in on the server submit the following query:
   
Select SYS.PROPS$.VALUE$ From SYS.PROPS$ Where ((SYS.PROPS$.NAME = 'NLS_CHARACTERSET')) ;

   Note: To perform this query you need to be logged in with SYSDBA privileges such as a system/manager

Superset	Subset
WE8ISO8859P1	US7ASCII
ALT24UTFFSS	US7ASCII

If ISO-8859-1 was used on the database server and CP1252 was used on the client the top two rows of character in CP1252 could not be stored in the database server. The server would save these characters as question marks.