Checkbox group insert and update values in one field

Hi,

This seems so basic but is not working. After I ran the DA wizard I updated a field to be a check box group of days of the week. I need to be able to select from one to seven of the boxes and have those values stored in that field. Dreamweaver sets up the group to have the days like this:

<label><input type="checkbox" name="Availability" value="Monday" id="Availability_0" />
Monday</label>
<br />
<label><input type="checkbox" name="Availability" value="Tuesday" id="Availability_1" />
Tuesday</label>...

and so on.

When I select multiple days the field only gets the last day selected.

What am I missing here? Is it a DW or DA tweak I need to make?

Thanks for any advice or guidance!