Espruino Wifi error

It is not clear where you enter this. It is expected to be in the editor / right hand pane of the Web IDE and then uploaded.

When you are connected to the Web / internet and do the upload to the Espruino board, your code is first parsed for modules required with require("..."). The modules are pulled from http://www.espruino.com/modules/ folder, for example -
in this case - either as EspruinoWiFi.js or EspruinoWiFi.min.js, uploaded to the Espruino board and stored in the Modules cache on Espruino board. After that, your code is uploaded. When it comes to execution of your code, require(...) will find the requested modules in the Modules cache and load/use them. If it cannot find them in the Modules cache, it tries to find a mounted SD card and looks for it there. If no card is mounted, the error message you see is what you get.