When you can't connect to your Mobile Terminal, there's a few things you need to double check or try it out when you couldn't pair:
1.) Make sure the network version is same, network version is the 4th digit from the version number.
For example 220.127.116.11 the 4th digit is 6, so it can pair with mobile terminal of version 18.104.22.168 and 22.214.171.124
(If you don't want to care about the network version, just make sure both ARMS F&B and Mobile Terminal is the newest version)
2.) Make sure both your devices are in the same WiFi network
3.) Restart your router.
4.) Use your iPhone 4 to create a WiFi network (you can refer here for the steps: http://support.apple.com/kb/HT4517) and connect your iPad to that WiFi and see if you can pair both devices. If this works, then may be is your router having problem.
5.) Relaunch both the mobile terminal app and the ARMS F&B.
6.) Restart both your Main Terminal iPad and your Mobile Terminal devices.
7.) In some cases, when you can't even pair, then you need to go to iOS Settings > General > Reset > Reset Network Settings.
8.) Try re-installing your Mobile Terminal.
9.) Try changing your wifi channels if your environment have many Wifi signals. Here's the instruction: http://www.pcadvisor.co.uk/how-to/network-wifi/3325316/how-change-wi-fi-channel/