I removed several external references (like base.Page_Load and Project) from your code-behind:
protected int status;
private void imgBtnShowAll_ServerClick(object sender, System.Web.UI.ImageClickEventArgs e)
{
}
private void imgBtnShowActive_ServerClick(object sender, System.Web.UI.ImageClickEventArgs e)
{
}
So it works ok here.
It looks like you're doing something wrong with treeview or page state. So treeview cannot find node by ID to apply client-side event to.