This problem is likely to occur if you have an older version of the Flash Player installed. the current version of Microsoft Installer, used to install REckon Accounts, can not work with this version of Flash Player.
Download the latest flash player from https://get.adobe.com/flashplayer/ and try again.
Look forward to you upgrading soon.
The name of the file downloaded from your website link is named Reckon Accounts Business Range 2018 R1. Can you confirm this is the correct file?
Yes you do have the correct file. After installing that one you will need to download and apply the Tax Tax update 2018 that will give you the updated Tax Tables for 2018-19 and make you STP compliant.
More importantly, what is your Operating System? The error message is indicating that a required component to install Reckon Accounts is incompatible with your operating system. Reckon 2018 requires Windows 7 and later versions.