Plug-in woes

I’ve been trying to install PointSetReconstruction tools in Rhino 5. However I get the message that states that it can’t be installed because the file comes from another computer and is blocked on my computer. However, when I go into the file properties there is no check box for unblocking the file!
What can I do?

Nick, In win7 its a button towards the bottom of the properties dialogue for the plugin file, not a check mark. But I just checked this myself and pointsetreconstructiontool.rhp did not give me any trouble installing with standard drag and drop. The properties for the file did not show any security buttons at all.
Try a rhino restart perhaps?