Previous versions of Blue Prism (upto 5 )used .NET remoting as a communication protocol which required trust between domains to be able to communicate between them. The fact that you need to tick that checkbox either indicates trust does not exist between domains or some other blocker on your network that is preventing .NET remoting from working.
I suggest engaging with network experts in your organisation to discuss your findings. In version 6 .Net Remoting has been superceeded by WCF