Alert message show again when i press browser back button

[neeraj]

Hi Everybody

I have one problem in my asp.net web application.
The problem is that I check the date validation in code behind;
if user not gives the valid data and press save button then I fire my
own exception by JavaScript alert message
Through register startup script
Like

RegisterStartupScript("Startup", "<script language=javascript>
{ShowError("'"& ErrMsg &"'") & "');}</script>")

It is working fine. But when user gives valid data and press save
button data getting saved in database and page redirect to other page
but when user press browser back button the previous alert message show
again.

I found on solution (Page Expire, but I don't want to do it)
I want to the java script message do not show again when I press
browser back button.

Any body can help me how can I do this.

thanks