Really odd this IOREF connection. After having a look at the schematic and the instructions* for the connection required if you are using a non R3 pinout board.... I became more confused.. As it appears that connecting 3.3 volts to IOREF causes NO level change as pin 19 is the B side VCC pin (connection to the Arduino pins). The instructions [copied below] suggest that one can make a permanent connection by soldering a jumper on the shield ...looking at the schematic reveals that this connects 5 Volts to the IOREF pin!! Huh????
Seeing that, I tried jumping 3.3V or 5.0V to IOREF and found both worked....Ah, I love electronics.
In any case, if a jumper is NOT installed when using a non R3 Arduino the shield will not work properly.
*"Using the Shield With Older Boards
If you are using the WiFi shield with an Arduino earlier than the Uno rev3, you need to make the connection below for the board to work. The WiFi board uses the IOREF pin on newer Arduino pin layouts (Uno rev3, Mega2560 rev3, and later) to sense the reference voltage for the I/O pins of the board to which it is attached. If you are using the shield with an older board, you need to connect the shield's IOREF pin to 3.3V. You can do this either with a jumper wire connecting IOREF to 3.3V as shown in the photo below, or by soldering the IOREF jumper on the bottom of the shield, shown below. WARNING: If you use the solder jumper, do not connect the shield to a rev3 or later board. To be safe, remove the IOREF pin on the shield. Otherwise, you will be shorting 3.3V to 5V through the IOREF pin."
David G.