Neal, IMHO (as many others) you have overestimating the forum capabilities
Yes, the forum may help, but it requires primarily you to do the job, starting from reading the manuals, recommendations and perform troubleshooting.
In addition to what Tom have said, I can point you to
system minimal requirements. Perhaps you were right to not opening the support ticket ... because compliance with minimal requirements would be the first thing support will ask you to do. Yeah-yeah, I know that it can work with Win7... either in less complex networking scenarios or your own network analysis capabilities.
Let me give you a clue: when you are saying "it's connected by a site-to-site VPN. All the ports are open for all traffic", do you mean you "believe", or you have a solid proof (aka wireshark logs) confirming that traffic (on all involved interconnecting points) over UDP ports 50000, 50001, 50002, 40000, 40001,40002, 40003, 40004 is routed and encapsulated/deencapsulated into site-to-site VPN correctly? (Also tell me that your are not using Win7-based site-to-site VPN...)
And IMHO following classic OSI model troubleshooting steps may help too. Starting with complete and detailed network diagram.
IMHO by the moment you have network diagram ready/analysed and traffic captured/analysed, you won't need forum help, because you will find it yourself
P.S. And please note that this is end-user forum. Where regular users are. Official tech support can be found via top menu of this page (fourth from top menu left) under Support-Technical Support.
P.S.S Last (at this stage, but not the least) thing Re: your 12Mb symmetrical connection:
Please note that this was measured with SS2 over 5 years ago, however still can be taken as valid.