Philip,
I wouldn't give up. I am confused. You say you have been using AC for six years. Yet, this problem seems like it is rather new. From what I gather, your network is a little unique or at least a bit complicated. Did you try one of my suggestions, which is to simplify everything and start with one or two computers.
Anyway, as the question on Experts-Exchange has not been able to bear any fruit, I have sent an email to one of the experts there. This expert is a SQL Server 2005 and 2008 expert. When I say expert, he is an EXPERT. I hope he emails back. He says he gets around 250 emails a day. I sent him the link to here and to the EE question and also inquired into his consulting directly. He states on his site that he does consulting for a decent price and can remote in and troubleshoot. He has answered over 5,000 questions on EE just in SQL Server 2005 alone.
Not to put down AC, as I stated before, it is difficult for them to help with the networking part. They are trained in the application and are at a disadvantage in that they probably aren't proficient at networking and possibly not even the inner workings of SQL.
I could tell you a story about my first month with AC and my partner and how crazy it was. Trust me, it was worse than what you are experiencing.
I am still not sure why you don't make a backup to .enc, and other multiple backups, uninstall v5 from the server as well as from SQL. Uninstall SQL Express and try the trial version of the full SQL Server 2005 Workgroup. Then reinstall.
Anyway, we shall see if he emails me back. I hope if he does you will give it a shot.
HTH Thanks.
