Don't use the button...

<asp:calendar id="myCal" runat="server" ... OnSelectionChanged="DoStuff"
/>


protected void DoStuff(object sender, EventArgs e)
{
// Do My Stuff
}

or do this ...

put label or a "placeholder" where you want your server control  to appear
in your page and dynamically add your control to that control at runtime..

i.e. (say you used a label called mycontrol).....

mycontrol.Controls.Add( yourservercontrol).

Did you just install the Oracle client? What version? We've had problems with
the 8.1.7 client. It never tells you that you have to reboot, but until you do
it won't work.

my Oracle client is 9i.
do you solve this problem? i have not find a method to
solve this problem.

Well I did a asp.net project earlier with oracle 9i as the backend. I
used OLEDB to connect to oracle.....btw, have u configures the listners
coz u cant connect to oracle without a listner on the client.....

i also used OLEDB to connect to oracle,driver is
"provider=msdaora.1",my aaa.aspx works on windows
xp,but now it does't work on a windows 2000 server. do
i need to configure the listners for connecting the
oracle?

Yes, u need to configure the listener on the new machine as well. My
connection string was as follows:
Provider=MSDAORA.1;Password=bmmiportal;User ID=bmmiportal;Data
Source=FIN_HO

Where FIN_HO was the listener I had configured to connect to oracle
which was on a remote site.