Vim not running inside tmux

When I try to open a file using vim inside tmux the whole window freezes. I have to kill the window with C-a &.

Here are my ~/.vimrc settings:

:set autoindent
:set ts=4
:set number
:set shiftwidth=4
:set showmode
:filetype on
:filetype plugin on
:syntax enable
:set mouse=a

and ~/.tmux.conf

# I like Ctrl-a as the default hotkey
unbind C-b
set-option -g prefix C-a

# Split window using | and -
unbind %
bind | split-window -h
bind - split-window -v

# Set status bar
set -g status-bg black
set -g status-fg white
set -g status-left ‘#[fg=green]#H’

# Highlight active window
set-window-option -g window-status-current-bg red

# Makes window numbering start from 1, instead of 0
set -g base-index 1

I am facing the problem in RHEL. However the same config works fine in my Mac. I guess, things were working fine till my RHEL box got restarted and I tried to recover a file in from vi swap file.

Any ideas on how to fix this?

[edit]: I tried ssh to other box inside tmux and running vi there. Works fine in remote box !

[added later]
Following the suggestion of @jasonwryan, I added the line set -g default-terminal screen-256color at the end of tmux.conf. That prevented programs like less from working.

echo $TERM inside tmux is "screen" and outside tmux is "xterm".

Searching for $TERM led me to https://wiki.archlinux.org/index.php/Tmux, from where I added the line set -g default-terminal "screen-256color" as the first line of tmux.conf. This made the $TERM inside tmux to "screen-256color". But now when I start vi inside tmux, it displays the following error:

E558: Terminal entry not found in terminfo
'screen-256color' not known. Available builtin terminals are:
    builtin_riscos
    builtin_amiga
    builtin_beos-ansi
    builtin_ansi
    builtin_pcansi
    builtin_win32
    builtin_vt320
    builtin_vt52
    builtin_xterm
    builtin_iris-ansi
    builtin_debug
    builtin_dumb
defaulting to 'ansi'

Looks like I have solved the issue. Just added set -g default-terminal xterm as the first line of my ~/.tmux.conf and it worked !