BI Publisher - configuration

Hi, Currently we have two test environments running on one server. Each environment has it's own database it is working off of. We are running one instance of BI Publisher on this server, so only one test environment can use it at a time. I am being told that if I want to allow both environments to use BI Publisher, I will have to separate the two test environments by placing them on separate servers. Each server could then run it's own instance of BI Publisher. I'm not sure why I can't run two separate instances of BI Publisher on the