Verify that you have installed the necessary components. Under the Help–>DigiESP for Embedded Linux section. On section 10.3 Including the wireless interface in the Linux Kernel, you’ll need to install the wireless-tools package and WPA supplicant package. This packages are necessary to configure the WLAN adapter. Also take a look at section 9.31.2 "Enabling the wireless network which shows you how to incorporate these packages in rootfs configuration.