the server is raising an error message - you should activate display_errors and set the iDebugMode in the config.inc.php to some value different from 0. It should show you an error message then - maybe you are missing some server requirement?
checkSessionChallenge() is rather a method than a variable,
here the shop checks no other session is mixed into the checkout process, which is crucial for order integrity and prevents stealing other session for the payment.
Well so in deed there seems to be a session issue on the new server you want to move
[QUOTE=ravindra;70723]
at the last step of checkout when I click on confirm order
then it goes to the blank page
not the thankyou page
but if I refresh that blank page, now the thankyou page has come,
and the confirmation mail do not goes to the admin.
[/QUOTE]
I had something similar to this happen to me once. Not from a server change but just from working with some mods to the order/thankyou page. That is, the first request would fail but if I manually entered the URL in the address bar I would get to the thankyou page. Maybe this is not at all the same as a refresh on your browser, but in case it is here’s what happened. It had to do with the eShop omitting GET data when a POST is received. So if the new server has some funky config that is forcing data into GET form, even though the order page submits a POST, then important vars may get dropped such as cl=thankyou.
In any case, may want to try some debugging that pays close attention to what happens to REQUEST data on the first request. If you find the that first REQUEST sets cl=start or empty in oxshopcontrol, this may be your prob.