HotKeyNet shouldn't have any problems with background input if you have adjusted your Sendmode Setting in the Options and are using the proper sendmode

http://hotkeynet.com/ref/send_modes.html

I haven't had any problems using HotKeyNet to send commands to games that require focus to receive input, like LotRO, or games that do not require focus, like WoW. It sounds more like it's not background applications having an issue, it's the connection to your other computers.

Do you have a copy of HotKeyNet running on each computer?
Are they all connected and loaded with your script?
Are the secondary computers set up as clients and the primary as master?

http://hotkeynet.com/p/doc2.html
http://www.dual-boxing.com/threads/2...e-to-get-going