I don’t know why, but it happens time to time. Suddenly wireless stops to connect. This time I could see all of the networks but was not able to connect to them. Some wrong “Bad password” problem appeared.

Here is a fast work around:

make sure that eth0 is properly defined in /etc/network/interfaces.

sudo apt-get remove wpa-supplicant

ifdown eth0

ifup eth0

sudo aptget install wicd

should be fixed now.