Hi ALAN JOHNSON,
Which browser do you used to open Silverlight application?
On Windows 10, Edge browser is not support Silverlight and you need to use IE which installed in Windows Accessories to open Silverlight application. And other browsers also don't support Silverlight any more. You could refer to the Compatiable browsers
and operating systems from below link.
https://www.microsoft.com/getsilverlight/locale/en-us/html/installation-win-SL5.html
If you are using IE, please check whether you have enabled Silverlight plugin through Tools -> Manage Add-ons.
Best Regards,
Weiwei
MSDN Community Support
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