ya exactly, I want to set nillable back to the button. I want to know in which situation we have to set it back. means in which condion we have to set nillable false and true...
Please see this link
http://www.sharepointblogs.com/dooke/archive/2007/08/14/the-xsi-nil-attribute-the-correct-way.aspx
and clerify me the condition in which we have to ...