Hi, I used to have the same problem. You may want to try to read topic 8. of the document at the following site: http://www.imm.dtu.dk/pubdb/views/edoc_download.php/502/pdf/imm502.pdf Hope it will help. Quan __________________________________ Do you Yahoo!? The New Yahoo! Search - Faster. Easier. Bingo. http://search.yahoo.com