This is not any problem that is inherent to the plugin, it is something specific to your machine. It is not perfectly clear to me, when you say that you uninstalled Silverlight 5, exactly what you did. So please follow these steps:
- Open Windows Control Panel > Programs and Features.
- Uninstall any and all versions of Silverlight that you find.
- Uninstall any and all versions of Maxwell for SketchUp that you find.
- Open C:\Program Files (x86)\Google\Google SketchUp 8\Plugins.
- Delete maxwell.rb and the maxwell folder, if they are present.
- Reboot the machine.
- Download and install a fresh copy of Silverlight 5, from here.
- Download and install a fresh copy of the Maxwell for SketchUp plugin*.
Regarding step 8, since you are cross-posting this both here, and
here, and because you say that the plugin is "back to demo mode," I am unclear on exactly which plugin you are trying to use. If it is the Standalone version, download a new copy from
here. If it is the Render Suite version, log into your account,
here, and download the appropriate version from the download area.
Please let me know if this helps. If not, it may be related to some problem with Internet Explorer on your machine, in which case, I would recommend making sure that your OS is properly updated (using Windows Update).