What is your database version? Is it 9.2.0.1? Do you have a user id that starts with a numeric character or reserved word? (example: create user "123" identified by one2three
If so, please take a look at Metalink note: 206512.1 -- EXP-8 and ORA-903 or ORA-933 When Exporting From Oracle9i Release 2 (9.2.0.1)