I have an enterprise license running 4 CMS6 sites under one instance of EPiServer which works fine. One of these sites is a Relate+ 2.0 site. We get the following issue: "License ###### is already active for a different instance on the current machine. "
This issue is negated if within IIS we start the Community site first, then visit it and log in, effectively initialising the license for this site. Then we start the other sites and the issue goes away. This isn't really a solution moving forward as the sites might get restarted by a Windows update or something and then if the Community site isn't the first site hit this error is thrown. Is there any way around this or is this because you cannot run Relate+ with a single CMS instance running multiple sites?
You must make sure to load any license on one site only. In your case, all sites load the Relate license, but only one accesses the API that the license enables you to access.
In your web.config, configure <episerver.community>'s <site>-element for the Relate site to point to the license you want to use there, using the licenseFilePath attribute on the <site>-element. Use a non-default filename so that other sites don't find your Relate license and loads it.