C# Visual Web Part button event not running

hello,

I have created a visual webpart and it is deployed in the site and it has two button ,one is to create a excel file using interop and download it by using filestream and responce.redirect ,once i clicked that button that button click event is running,but when another button in the same page is clicked its button event is not running.

if i refresh that page and click that 2nd button it is running that button event.

please help.

thanks