<asp:button onmouseover="this.style.cursor='hand' > not working

[Aruna]

<asp:button id="Button9" onmouseover="this.style.cursor='hand' runat="server"
Width="119px"></asp:label>


I am getting error at onmouseover.
But it is working fine for HTML element <INPUT>.
Why it is not working for <asp:button> ?
Is it necessary to import any namespace?
Can anybody give code?