once i clicked on "Proceed to checkout" button, we are getting below error
The sitename.com is't working
www.sitename.co.nz is currently unable to handle this request
Http Error 500
even in backend when we open some orders, than also same error in order-view page.
we have shared hosting.
It was a problem with magento core file cc.php file , one of our devoloper edited it in wrong way, once i replaced the original file, it worked fine.