3D slicer 4.10 can't load structures

Operating system:windows 10
Slicer version:4.10
Hi 3D slicer experts and all
I installed 3D Slicer 4.10 ; but unfortunately , when I load structures the following error message is shown.(figure 1) ; and the CT images are not displayed(figure2). also, I can’t install any Extension from Extension Manager. Can you help me about these problems.
Thanks a lot

You need to install SlicerRT extension to be able to load RT structure sets.

thank you for your guideline. but I can’t install any Extension. can you help me?

See installation instructions here. Name of the extension that you need to install is SlicerRT.

I’m sorry for my questions! but my problem with installing Extensions is that the page associated with Extension Manager is like the following figure ; and no Extensions are visible for selection . I installed and uninstalled the slicer several times, but it was not effective. please guide me.
thank you

Is it an official Slicer-4.10 build? Is it possible that your computer is behind a firewall?

Anyway, you can follow these instructions for downloading an extension using a web browser and installing it manually.