ORA-01704: string literal too long
Whenever you try to insert a string >4000 chars

Date: 2006-05-03 00:38
Sender: Kubo Takehiro

If you use DBI, see:
   http://www.jiubao.org/ruby-oci8/dbd_oci8.en.html

If you use oci8 high-level API, how to insert CLOB is not documented.
But it can be done same as BLOB.