Setting All To False

I've got a form which shows all the records in a list, with a check box next to each which is for choosing which ones to print. i have created a "de-select all" button, using a macro with simple SQL behind it -

"UPDATE companys SET print = false WHERE print = true"

when i test this button, it sets all the boxs to false except for the last one that was set to true. it also doesnt update the form straight away, sometimes the checks say until you scroll so the record is no longer on screen.

does anyone know how to rectify these problems?

Thanks