From the UDI Wiki:
ISY Launcher cannot find ISY
Make certain that you are using ISY Launcher. This is a MUST
If you have VPN software running, Admin Console cannot search for ISY on your computer. Please disable the VPN, find ISY's IP address and then click the Add button and enter it manually
Make certain that, after reboot, the pattern of lights is as described here
If you have recently changed your modem/router, please follow these instructions
If you have any firewall software, make sure it's configured properly
If all the above have been checked, it's almost a guarantee that that your ISY is not on the same network as your computer. Perhaps at some point you might have configured ISY with a static IP address. Or, that your WiFi network is not connected to the wired network.