max_allowed_packet mysql

Hi    I am using rails 2.3.8 with mysql 5.1. In my attachment model the validation was   validates_attachment_size :attachment, :less_than => 2.megabytes, :message => "Upload file size should not exceeds 2 MB"

And my /etc/my.ini has

max_allowed_packet = 16M

        The above worked perfectly. But now I need file limit size as 10 MB instead of 2 MB. So I changed validation like   validates_attachment_size :attachment, :less_than => 10.megabytes, :message => "Upload file size should not exceeds 10 MB"

And now when I tried to attach a file with size 9.2 MB it gets stuck for long. No attachment happens. Please help

Thanks Tom