I've inherited a project that is using some old code using the v1 API. The weird thing is that this test code works on my laptop, a dev server, but not on the production server. Before I go to the server administrators I was hoping that someone could check out this code for any possible problems. The server that it's on is a locked down server that is managed for PCI compliance, so they are very concious about security. Anything that comes to mind from a server standpoint?
After reviewing your code, the first thing that I would suspect that is a server related issue is that the SSL root certificates for the production server are out of date. I have seen cases where this can cause Constant Contact's SSL certificate to appear invalid, thus causing any cURL requests that use SSL to fail.
Beyond that, you can try getting more information about the error back from cURL and see if there is an error message that you can use. in PHP this can be done using curl_error().