I have tmux 1.5 installed on a couple of Ubuntu machines and I have this in my ~/.tmux.conf:
unbind-key C-b set-option -g prefix C-\
So, on a couple of RedHat machines I have ssh access to (but not root) I compiled tmux 1.6 and installed it in my directory. Now when I try to set C-\ as my prefix, I get this on startup:
/home/user/.tmux.conf: 2: line continuation at end of file
Obviously its not parsing the file correctly. As a test I change it to:
unbind-key C-b set-option -g prefix C-'
And I get:
/home/user/.tmux.conf: 2: invalid or unknown command: set-option -g prefix C-'
So it's still not parsing correctly.
However, this does work:
unbind-key C-b set-option -g prefix C-o
So it seems to be a problem with non-alphanumeric keys.