If I uncheck a checkbox can why wont it clear the field? (value list has one Item in it)

Probably because you are attempting to approach the solution as if you were handling it peer-to-peer. But yuou are trying to get a format file to interact with the database.

Have you considered approaching the solution using a calculation field [text, unstored] on your web layout in conjunction with an html radio button:

case(fieldname="","In", "Out")

? Where fieldname could be the radio button field of the peer-to-peer solution. Or it could be another field such as a unique identifier (UID).

Try adding this just after the [FMP-Valuelist]...[/FMP-ValueList] tags:

<input type="hidden" name="FieldName" value="">

FieldName is the name of the field you're using with the checkbox. The idea here is that if the checkbox is unchecked, the form will force an empty value into the field.

Hope this helps -- let me know!

Perfect, thank you!