Have you been copying plugins from older versions ?
This is not advisable - many were updated to suit Ruby2 used in the newer SketchUps…
Get the latest versions wherever possible.
Where did you get this version of ‘Flattery’ from ?
The older Flattery version [on its website] is incompatible with the newer SketchUps.
Under its copyright license I did update the script hosted at SketchUcation’s PluginStore, to make it compatible.
You should get the RBZ from there and install it using the SketchUp > Preferences > Extensions > Install… button…
Here’s a link:
I’m sure Jim Foltz will comment about his oldie ‘Unfold’ - which is available through his own web-site…