Help - Why does insert only work once?

[wxdqz]

Hi, I have a php form that gathers data then inserts it into a table. Once the form is submitted the user has the choice of entering another set of data and the form is reset. It works fine for the first insert but after that the command is ignored. What might I be doing wrong?

INSERT INTO recipients (id, first, last, email, company, user, message) VALUES ('', '$first', '$last', '$email', '$company', '$user', '$message');

nb: Once I open another browser window I can enter another form

Thanks

Richard