Comment 2 for bug 210005

See http://wiki.debian.org/iwlwifi

It seems you need to run "ip link set wlan0 up" before setting the ESSID. From that url:

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If the card accepts the essid, for example, by doing

iwconfig wlan0 essid YourESSID

but does not associate to the access point even when no encryption is
needed: The driver seems to need the interface to be in the up state
when it gets the essid. So first do

ip link set wlan0 up

then set the essid as before.
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It is working for me with this.