I am attempting to setup PayPal's Website Payments Pro with ZC but I keep getting a 10501 invalid configuration - invalid merchant configuration warning when attempting to check out. I ran the debug mode and the only thing listed as a "failure" is the ACK:

[AMT] => 0.01
[CURRENCYCODE] => USD
[TIMESTAMP] => 2008-07-01T20:02:55Z
[CORRELATIONID] => b4dd9a6ab1ecc
[ACK] => Failure
[VERSION] => 2.3
[BUILD] => 600904
[L_ERRORCODE0] => 10501
[L_SHORTMESSAGE0] => Invalid Configuration
[L_LONGMESSAGE0] => This transaction cannot be processed due to an
invalid merchant configuration.
[L_SEVERITYCODE0] => Error
[CURL_ERRORS] =>

I don't know what ACK means so I can trouble shoot this error.

I've been combing over the site for days trying to make sure the SSL is happy, that all the information is exactly the same between PayPal and ZenCart, etc. so any help would be much appreciated.

Two other questions:
I have cURL set to "true" but have no cURL proxy address set since the server owners say it's "not necessary". Will PP WPP still work without the proxy address?

To run PayPal's Website Payments Pro I just need two modules installed - Website Payments Pro and Express Checkout, right? I don't need to setup IPN also?

Thank you!