Case of gnutls_handshake() failed: A TLS warning alert has been received.

I would appreciate any advice about this TLS warning situation:

I am calling a REST API via https with pretty standard parameters: https://api.social123.com/services/socialdata.php?rquest=searchcontactpoints&key=xxx&first_name=xxx&last_name=xxx&content_mention=NULL-NULL

Entering this URL in a browser (with an appropriate API key) yields the expected JSON result.  When I try this in PHP on our server, I get "gnutls_handshake() failed: A TLS warning alert has been received" from curl_error().  I've read online about this error message, but I can't figure out what's happening in this situation.

A verbose error trace yields:

* About to connect() to api.social123.com port 443 (#0)
*   Trying 198.199.79.238... * connected
* Connected to api.social123.com (198.199.79.238) port 443 (#0)
* found 141 certificates in /etc/ssl/certs/ca-certificates.crt
* gnutls_handshake() failed: A TLS warning alert has been received.
* Closing connection #0

From this code:

  $ch = curl_init();
  curl_setopt($ch, CURLOPT_URL, $url);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
  curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
  curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
  curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
  curl_setopt($ch, CURLOPT_MAXREDIRS, 4000);
  curl_setopt($ch, CURLOPT_TIMEOUT, 30);
  curl_setopt($ch, CURLOPT_STDERR, fopen($path, 'w+'));
  curl_setopt($ch, CURLOPT_VERBOSE, 1);
  $json = curl_exec($ch);
  $errmsg = curl_error($ch);
  curl_close($ch);

(The high MAXREDIRS and TIMEOUT values were recommended by the social123 API provider; I don't think they matter to this problem.)

I cannot create or modify /etc/ssl/certs/ca-certificates.crt directly, but I can look at it, and indeed there are 141 certificates in that file.  Am I hitting a limit on the number of certificates that this cURL version will handle?  If that's not the issue ... how can I find out more about the reason for the TLS warning alert?

This is running on a server where I have limited control. 
phpinfo() shows:
libcurl/7.19.7 GnuTLS/2.8.5 zlib/1.2.3.3 libidn/1.15
PHP Version 5.2.17 on an Unbuntu OS

Thanks in advance.


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