I had the same problem and this is how I fixed it:
* shutdown NetworkManager, e.g. with 'sudo kill -2'.
* backup your /etc/network/interfaces:
sudo mv /etc/network/interfaces /etc/network/interfaces_bak
* restart NetworkManager:
sudo /usr/sbin/NetworkManager --pid-file /var/run/NetworkManager/NetworkManager.pid
Apparently NetworkManager is a little flaky with certain entries in the interfaces file.
I had the same problem and this is how I fixed it:
* shutdown NetworkManager, e.g. with 'sudo kill -2'.
* backup your /etc/network/ interfaces:
sudo mv /etc/network/ interfaces /etc/network/ interfaces_ bak
* restart NetworkManager:
sudo /usr/sbin/ NetworkManager --pid-file /var/run/ NetworkManager/ NetworkManager. pid
Apparently NetworkManager is a little flaky with certain entries in the interfaces file.