ORA-01460: unimplemented or unreasonable conversion requested error

Am getting *ORA-01460: unimplemented or unreasonable conversion requested error when inserting byte array value to Oracle DB. In DB column data type is BLOB, tried to insert with plsql block as well as direct insert query, still getting same error. Note: I can insert data with less than 13kb not more than that. And PDF file am converting to byte array before sending to Oracle. Looking for help on resolving the issue. Thanks