Received warning message when clicked on the submit button

When clicked on the submit button to change pw, logout, submit a page, etc..., I kept receiving the below message:

warning: Cannot modify header information - headers already sent by (output started at /homepages/10/d144739142/htdocs/modules/book.module:1) in /homepages/10/d144739142/htdocs/includes/bootstrap.inc on line 695.

What do I need to do to fix this problem?

Thanks

trantt