We have a PDF generated from an .XDP using Livecycle 7.2.1. It submits without problem on any Windows/Reader combination but fails on 3 Macs that I have tried. The Macs are running Snow Leopard and I have used a range of Reader 9.4.4 to X.
Interestingly, a web service call, which precedes the http Submit, is working find. Any ideas?