Manuel,

It is recommended that you use a single version of the toolset in your web site to avoid reference conflicts.

Since referencing multiple versions of the controls will each require different versions of the shared assembly, they will not be able to be used at the same time.  You can add a web.config to a sub folder of a web site and in that web.config remove the assemblies referenced by the parent/ancestor folder and add assemblies for a different version of the toolset to allow you to use multiple versions of the toolset on a single web site.

While this would allow you to use two versions of the controls on a single web site, I expect that you wouldn't be able to use skins for the controls in the child folder as the skin files would reference a different version of the toolset than the pages in that folder are using.

Please also note that this approach will only work in the assemblies are in the GAC rather than the local bin folder for the web site.

Let me know if you have any questions with this matter.

Alan