It's easier to use the TO_LOB function like:

-- Your old table
CREATE TABLE long_table (n NUMBER, long_col LONG);

-- The new table
CREATE TABLE lob_table (n NUMBER, lob_col CLOB);

-- Load the data into the new table
INSERT INTO lob_table
SELECT n, TO_LOB(long_col) FROM long_table;

See: http://otn.oracle.com/docs/products/...tion.htm#84934

Cheers