Disclaimer: This is plagiarized! See: http://www.anysql.net/en/oracle/oracle_bug_exp00003.html

When you use old version of exp to export tables with LOB column from Oracle 9.2.0.5 or higher version, you will get an error "EXP-00003 : no storage definition found for segment .....", actually this is an Oracle bug, you could temporary get it resolved by replace a view "exu9tne", as following:

Before exporting, run the following SQL under sys:
CREATE OR REPLACE VIEW exu9tne ( tsno, fileno, blockno, length) AS SELECT ts#, segfile#, segblock#, length FROM sys.uet$ WHERE ext# = 1 UNION ALL SELECT * FROM SYS.EXU9TNEB /
After exporting, run the following to restore the view definition according to Metalink Notes.
CREATE OR REPLACE VIEW exu9tne ( tsno, fileno, blockno, length) AS SELECT ts#, segfile#, segblock#, length FROM sys.uet$ WHERE ext# = 1 /