The problem here is that expected files are not there when called. Looks like u have a number of such instances such as:
Warning: fopen(/570732-2-data.txt)
Warning: file_get_contents(/570732-2-signed.txt)
Warning: file_get_contents(/570732-2-encrypted.txt)
One possible reason for this is the permissions set on the directories, set them all to 777 will fix the problem.
However looking at your error messages I think the files in your case are not being found as you have not set the directories up in the first place. Here is what I would try:
Step One
ftp your site and create some directories to hold the files, any will do, such as for example:
in the public_html directory create: keys
then in the keys directory create: public_cert, private_key, paypal_pub_key and temp.
Step Two
Now copy your public certificate into the public_cert directory, your private key into your private_key directory, the paypal public key into the paypal_pub_key directory, and leave the temp directory empty.
Step Three
Set the permissions on all the directories you have just made to 777
Step Four
Now go to admin->modules and click the Credit/Debit Card (via PayPal) module and enter the following:
under "your private key" enter:
/home/sites/xxxx.co.uk/public_html/keys/private_key/whatever_u_have_called_yr_key.pem
under "Your Public Certificate" enter:
/home/sites/xxxx.co.uk/public_html/keys/public_cert/whatever_u_have_called_yr_pub_cert.pem
under "PayPals Public Certificate" enter
/home/sites/xxxx.co.uk/public_html/keys/paypal_pub_key/paypal_cert_pem.txt
under "Your PayPal Public Certificate ID" enter
code given to you by paypal
under "Working Directory" enter
/home/sites/xxxx.co.uk/public_html/keys/temp/
under "OpenSSL Location" enter
/usr/bin/openssl
That should fix yr problem. For anyone else wondering exactly the correct path to reference the directories you make then look at the error message and it is the same as the start of the path for the paypal_ipn.php file ie higlighted in red for this case here
Warning: fopen(/570732-2-data.txt) [function.fopen]: failed to open stream: Permission denied in /home/sites/xxxx.co.uk/public_html/catalog/includes/modules/payment/paypal_ipn.php on line 426
Hope this helps you