New Post: Setting directory security

I am trying to create an MSI for an Outlook add-in, which requires that the MSI creates a directory under "C:\Program Files (x86)" and grants full permissions to all users to this directory.
So far I have tried:

        Dir rootDir = new Dir(targetPath, installedfiles);
        DirPermission permissionsToAll = new DirPermission("Everyone", GenericPermission.Execute | GenericPermission.Read | GenericPermission.Write);
        DirPermission[] allPermissions = new DirPermission[] { permissionsToAll };
        rootDir.Permissions = allPermissions;

...which results in the wxs:

<Component Id="Component.1" Guid="8208b126-5129-4018-8106-83ddc6c27eee">
      <CreateFolder>
        <util:PermissionEx User="Everyone" GenericAll="yes" />
      </CreateFolder>
    </Component>

When I run the MSI (I am an Administrator on this machine), I get a system error (-2147024891) on the directory ""Failed to set security descriptor on object".
Any idea?