This error is due to the execute grant missing on DBMS_EXPORT_EXTENSION

Error

test*TESTDB1:/home/oracle>exp menu file=export.dmp tables=test_table1 log=export.log

Export: Release 11.2.0.3.0 – Production on Thu May 24 10:46:42 2012

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Password:

EXP-00056: ORACLE error 6550 encountered
ORA-06550: line 1, column 15:
PLS-00201: identifier ‘SYS.DBMS_EXPORT_EXTENSION’ must be declared
ORA-06550: line 1, column 15:
PL/SQL: Statement ignored
EXP-00000: Export terminated unsuccessfully

Fix

To get round this error you need to

GRANT EXECUTE ON DBMS_EXPORT_EXTENSION to PUBLIC;

You can now run the export with no errors.