In the database, look for the settings below:

select * from props$;
nls_lang=american
nls_territory=america
nls_charaterset=we8dec

Then do
on UNIX
export NLS_LANG=AMERICAN.AMERICA.WE8DEC
on NT
set NLS_LANG=AMERICAN.AMERICA.WE8DEC

Then run the export

HTH
Amar