As I said, its a vte bug. Look at the bugzilla link I provided.
On Tue, Dec 6, 2011 at 16:18, Jai Dayal <email@example.com
> I should have been more clear: yes, I am using emacs -nw when ssh-ed into
> the servers.
> However, on my local machine, there is a graphical emacs (23.2.1) and when I
> do alt-x, it works as expected (M-x)
> So the problem only happens over ssh connections
>> Are you using emacs in the terminal (emacs -nw)? There was a bug in
>> vte which caused Alt keys to be neglected for all gtk based terminal
>> emulators with the latest version of gtk. Several distros were
>> affected (e.g. Debian). If my description matches your problem, see
>> comment 20 on this bug report