flash player not enabled to open

the flash player is not enabled

This is a content and/or browser issue, not Flash Player itself.  Supported browsers disable/block Flash by default, forcing the user to enable it for each browsing session.  Content developers must ensure their Flash detection scripts wors with the browser Flash detection requirements, allowing the browser to detect the content requires Flash and prompt the user to enable Flash.  

You don't mention which browser you're using, see https://helpx.adobe.com/flash-player.html for instructions on enabling Flash in supported browsers.  If those don't work, I recommend contacting the content provider with your issue.

Also, sounds like some MyMaths' content no longer requires Flash, and the content provider is working to update their content so that it no longer requires Flash (source: https://support.mymaths.co.uk/technical-support/what-mymaths-content-has-been-updated/and https://support.mymaths.co.uk/technical-support/flash-free-mymaths/)