SQL Server 2005 bit datatype problem - ASPRunner.NET 4.0 (Build 169)

Hi, I've a problem with bit datatype in SQL Server 2005.

In edit page, the code that updates field is:
e.InputParameters["ArPubblicato"] = fldEditArPubblicato.Checked;
So, if value is 0 and in edit page I set the value to 1 (checking the checkbox), update runs correctly. If value is 1 and I try to set it to 0 (checkbox not checked) the value in the table field is always 1. Why?
Thank's to all, and excuse me for my bad english!
ginik.