I had the exact same issue a couple of months ago. Support gave the answer to check the <automaticSiteMapping> in episerverframework.config that your machine is listed there. This solved the problem for me.
You are correct Andreas that resolved the issue entirely. It was only when i did clean installs and there was no automaticSiteMapping for the site on the computer that this happened. Still seems very strange to me that this would be the case as without page providers the site still starts and episerver is able to add the automaticSiteMapping itself.
I have an issue with an CMS6 R2 enterprise site with multiple page providers wherein during a full rebuild the site will throw the error:
An Enterprise license is required in order to add a PageProvider
And the site will not start even if an Enterprise license is present in the folders for the site, and the configuration value is set in the Episerver.config.
The only way to resolve the issue is to remove the PageProvider values from the Episerver.config and try to access the site. When this is done the site starts as usual and all EPiServer components are initialized. After this we add the PageProviders again to the Episerver.config and visit the site. This time everything works as usual and the Page Providers are loaded.
In the episerver.config the licensefile location is set to simply : "License.config"
Once when this error was thrown i did these steps:
Removed the licensefile from the website folder and put it in a temporary folder
Removed the Page Providers from the episerver.config
Tried to access the site.
This time the site threw a licensing error but instead said:
Cannot find licensefile C:\License.Config
Ater putting back the license.config in the webroot and trying to access the site again this error was no longer thrown and the website launched as usual.
This leads me to believe that there is an issue with some of the Startup components for episerver trying to acess the licensefile (probably to check if its an enterprise license or not) and instead of looking for the licensefile in the webroot its trying to acess it directly through the filesystem (hence the C:\License.Config error).
Is this a known issue and is there a work-around of some sort? Do i need to have absolute path's to the Licensefiles in my Episerver.config instead of relative ones ?