Synchronous AJAX call fails on iPad, but not other platforms and browsers

Does anyone know why a synchronous ajax call would fail and give the following error on Safari on an iPad, but the same code works fine on all other platforms and browsers I'v开发者_开发问答e tested so far?

NETWORK_ERR: XMLHttpRequest Exception 101: A network error occurred in synchronous requests.

That error suggests that I'm attempting a cross-domain request, but I'm not; the requested URL is on the same host, and in fact it's a relative URL. Even in trivial tests, this fails on the iPad (and works on all other platforms and browsers, including Safari), so I'm confident I've ruled out any possibility of a time out.

Also, the same request, if made asynchronously, works perfectly on the iPad; it's only synchronous requests that give the 101 exception. It's driving me crazy!

One more bit of detail: this only happens on my production server. The synchronous ajax call actually works fine on my development server. Both servers require the same client certificate... so I don't think there's any difference there. I can't think of any difference between the two servers that could have an effect here.

Any insight into this problem would be greatly appreciated. Thanks!

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It turns out the key difference between our development and production systems is the certificate requirement.

The issue turns out to be a problem with the way XMLHttpRequest.send() on the iPad version of Safari processes a synchronous request on a domain that is certificate-protected. I can't explain the internals of the method, but somehow it has a problem and throws the 101 exception, believing it--apparently--to be a cross-domain request. Again, the same request made asynchronously on the same certificate-protected server works just fine. Frustrating case, and one with no solution!