Thanks for the sample, this helps us to quickly fix this error.
Now you can use following workaround of this problem:
[c#]
void Form1_ButtonClick(object sender, NineRays.Windows.Forms.Data.NodeBase node)
{
if (node != null) // if node == null this is 'false' firing of this event on empty FlyGrid.
{
MessageBox.Show("Click");
}
}
PS: fixed version of FlyGrid will available at the end of this week.