in updatepanel gridview rowcommand event occur only once

I have a grid view in an updatepanel where i have 4 items

1) BOund Field

2) Button Field -- SHowing another grid

3)Button Field ---- opening a  popup

4) Button Field --- Deleteing the selected row

All these three button fields are working fine but the row command event is occuring only once

What is the solution to this problem

Following is the property of update panel

<asp:UpdatePanel ID="upCMStationList" runat ="server" ChildrenAsTriggers="true" UpdateMode = "Conditional">