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.