Usually this is a networking issue and you are loosing connectivity for brief periods of time and don't realize it. I just came from a system that insisted everything was good to go, but they were using AT&T's sticky static IPs.... not really permanent IPs even though they say they are. Also, DSL connections are infamous for dropping and reconnecting. I would start by hosting it somewhere cheap for a short period of time and testing it if is working well from a hosting location. If so, then you know your local network is not up to snuff for commercial connections. That is not uncommon.
Network trouble shooting involves substituting wires, routers, switches and testing inbetween each change. You can run router pingers that constantly send a ping and when the connection drops, it records the drop so you can use it to show your ISP. Many ISPs will run this for you for a short period of time (few days) if you request it.
Tell us more about your network and ISP?
Have you check to see if it is a licencing issue? Maybe you have too many concurrent connections?
Thanks for your comments,
In reply to Keywords, i have checked the concurrent connections and these arent being exceeded.
In reply to Taylor Sharpe, i have had the BT engineer out today, he has replaced all of the networking hardware and suggested that he thought that there was a fault with it. I'm dubious as to his diagnosis and think that your suggestion of a residential connection not being of a high enough quality for commercial use may be to blame. Im going to monitor the effects of the hardware changes over the next few days to see if they have made a difference, and if they havent im going to try a Server Hosting company for a month as you suggested to see if this solves the issue.