Scaling in Layout - 2019 version

Please please help if you can! I have been trying for the last few hours to do something that I feel should be simple, but sadly I am failing every time. I am trying to send a scene from Sketch Up to Layout and scale it to size. There are two things - it doesn’t show a classic scale of 1:25 in the scale bar so I have customed this in Preferences, and this is the size I need. However when I try to select the image in Layout to scale it, it just doesn’t work, it comes up with an exclamation symbol. I am sure I am missing something obvious but I can’t figure it out. If you can help I would be grateful. My end goal is to draw a floor plan in detail on Sketch Up then scale it to 1:25 in Layout. Thank you!

The most obvious question: is the inserted scene in Parallel Projection mode?(standard views are automatically in PP). If not, then you can’t set the scale.

If you’re sure that the scene is in PP, and you’re able to select the desired scale in the dropdown list — but you’re seeing the exclamation mark in the corner of the viewport — then simply select the viewport and hit the ‘Render’ button on the ‘SketchUp Model’ tray. (or tick the ‘Auto’ render button)

Thank you db11 I will give that a go and hopefully this will crack my confusion over it. Thank you!