when im trying to install appassure agent in a windows server 2008 R2 server i got the error below.
AppAssure went End of Life in 2018 and is no longer supported. Please upgrade or use a Rapid Recovery Agent for new installs.
As for the 416 Error, this is an HTTP error. Please make sure you are using a full Agent installer, not a Web installer. Make sure the required services for the AppAssure / Rapid Recovery Agent are running and not Disabled. If they any of them are stopped, start them and verify that they can be started successfully. As per KB article: https://support.quest.com/kb/218896/required-services-for-rapid-recovery-and-appassure
You cannot. The agent has to be the same version as the core or it can be an older version than the core. So in your instance if you are using AppAssure 5.x for the core, the agent you install needs to be the same 5.x version as the core. Unfortunately that version is end of life and we no longer provide support or downloads for it.
As Henrik said, double check and make sure you aren't using the web installer. If you are using the web installer, it needs to have access to the internet so that it can download the necessary installation components.