Why doesn't this work????

using (AppSecurityDataContext dc = GetDataContext())
{
    tblUsersInApplication uia = new tblUsersInApplication
    {
        UserId = um.UserId,
        ApplicationId = LoginCredentials.ApplicationId,
        LastLoginDateTime = DateTime.Now
    };

    try
    {
        dc.SubmitChanges();
    }
    catch (Exception e)
    {
        Error = e;
    }
}   

I get no exceptions. Runs fine. The date/time doesn't show up in the SQL table after it runs.