Chances are you do not have sufficient access-rights to add/change files/subfolders in your SketchUp Plugins folder... By default Windows will probably have limited you to have Read-only access, because the Plugins folder is within the 'Program Files' folder 'tree'... BUT you will need Read/Write [FULL] rights to add/change its files/folder... So... you need to find your Plugins folder's icon...*** Select it, right-click > context-menu > Properties > Security > Edit... Ensure everyone/every-group listed [of course including yourself] have FULL rights to that folder... You might have to have admin-rights to change this... Ensure that these FULL rights 'trickle-down' to all of its contained files/subfolders... Also check that the owner of the folder has similar rights, if not perhaps try changing its owner to be 'you' ? ***You are on a PC so depending on your OS your Plugins folder should be in C:/Program Files/../Sketchup../ But copy+paste+<enter> this code into the Ruby Console if you are not completely sure... Sketchup.find_support_file('Plugins') it'll return somethings like... C:/Program Files/Google/Google SketchUp 8/Plugins Other related SketchUp folders that you might want to write to from time to time... include Components, Materials and Styles... which should also have FULL permissions set...

That is the error message you get when trying to install an old version of the plugin. Where did you get it! Go to the PluginStore at the top of the page and install the latest version from there. Also install the latest version of Libfredo. Better still, install the pluginstore tool itself and auto install the plugins you want from within sketchup.