In case your web browsers can't access the RuneUI via Wifi after finishing setup RuneAudio in Raspberry Pi 2, connect the wireless router and Raspberry Pi with LAN cable and enter http://runeaudio.local or IP address of RuneAudio (Wired connection). If RuneAudio is accessible via wired connection, you have to take a look at your wireless router's settings.
MultiAP Isolation could have blocked RuneAudio wireless connection
MultiAP Isolation or Access Point Isolation is a wireless router features that provides an additional layer of security for users of the hotspot by preventing connections between devices in the network. That says, keeping the devices in the network to be invisible to each other.
MultiAP Isolation is less important in home network unless you have a number of visitors that connect your network frequently.
How to disable MultiAP Isolation
For D-Link wireless router, go to Setup > Wireless > Wireless Basic > unchecked Enable MultiAP Isolation and then click Apply button.
The steps are more or less the same in other wireless router's Wifi settings. You may have to check the availability of this features on the wireless router user guide.