I had a setup with 2 virtual hosts via SSL on the same server, but when trying to add a third i couldn't get it to work. Turns out using named virtual hosts is guaranteed not to work with SSL, and this was SSL. So why did it work for 2 virtual hosts before? This was because the domain names were pointing to different IP addresses. (One to the load balancer and one to one of the two balanced machines.)
Lesson learned: read the ouput of 'apache2ctl -S' carefully!