AspxAutoDetectCookieSupport=1 and paypal PDT

I have two Winhost sites one hosted on win2008 and one on win2012,
one on 2012 is 4.5 framework,

the site on win2008 appends AspxAutoDetectCookieSupport=1 to the end of the url and the win2012 doesn't,
I have the same coding on each site to allow for paypal PDT the only difference i can see is the AspxAutoDetectCookieSupport=1 appended, the site with AspxAutoDetectCookieSupport=1 works fine where the other one states "The parameter is incorrect" ,
How do i modify the web.config to append AspxAutoDetectCookieSupport=1,


I think this is all that is wrong i hope but if you have have similar problems i keen to hear your ideas


http://xxxxxxxx.co.nz/ppreturn.aspx...15&item_number=&AspxAutoDetectCookieSupport=1
http://xxxxxxx2.co.nz/ppreturn.aspx...leted&amt=22.50&cc=USD&cm=1000016&item_number=