This error means that eWallet on your PC is unable to connect to eWallet on your iPhone to synchronize. The most common causes are:
An active VPN connection on your desktop PC
Multiple connected networks on your PC, i.e a cable connection to a wi-fi router as well as a wireless connection, or a cable connection to one network and a wireless connection to your wi-fi network.
A firewall - or other network security software - that tries to block programs on your computer from making outgoing connections. Make sure network security software has an exception to allow eWallet to communicate on all ports.
A firewall - or "wireless isolation" or "AP isolation" setting - on your wi-fi router
A temporary problem with your Apple device or your wifi router. Try rebooting both of them (turn them off and back on).