On Linux Ubuntu 11.04, after each command (cd, ls, vim...) successful or not, tmux prints out as a last line ps1_update: command not found.

Is there any config option I am missing?

Thank you very much!

tmux.conf

# http://lukaszwrobel.pl/blog/tmux-tutorial-split-terminal-windows-easily
# just remember that after every modification, tmux must be refreshed 
# to take new settings into account. 
# This can be achieved either by restarting it or by typing in:
# tmux source-file .tmux.conf


# Here is a list of a few basic tmux commands:

# Ctrl+b " - split pane horizontally.
# Ctrl+b % - split pane vertically.
# Ctrl+b arrow key - switch pane.
# Hold Ctrl+b, don't release it and hold one of the arrow keys - resize pane.
# !Ctrl+b c - (c)reate a new window.
# !Ctrl+b n - move to the (n)ext window.
# Ctrl+b p - move to the (p)revious window.
# Shift+LMB - select text.
# ALT+Arrows to move among panes.



# rebind default prefix to C-a
unbind C-b
set -g prefix C-a

# use ALT+Arrows to move around panes
bind -n M-Left select-pane -L
bind -n M-Right select-pane -R
bind -n M-Up select-pane -U
bind -n M-Down select-pane -D

# activity monitoring
setw -g monitor-activity on
set -g visual-activity on

# highlight current pane
set-window-option -g window-status-current-bg yellow

# enable pane switching with mouse
set-option -g mouse-select-pane on

# read bashrc
source ~/.bashrc

# Sane scrolling
set -g terminal-overrides 'xterm*:smcup@:rmcup@'

commandline print out

($(cat)user@tiki:~/.vim$ ls
autoload  bash_profile  bashrc  bundle  README.md  tmux.conf  vimrc  xmonad  xmonad-ubuntu-conf  xsessionrc
ps1_update: command not found
($(cat)user@tiki:~/.vim$ ll
total 56
drwxrwxr-x  2 user user  4096 Mar 17 10:20 autoload/
-rw-rw-r--  1 user user   170 Mar 17 10:20 bash_profile
-rw-rw-r--  1 user user  4004 Apr  2 11:37 bashrc
drwxrwxr-x 20 user user  4096 Aug 20 10:55 bundle/
-rw-rw-r--  1 user user 11170 Aug 20 11:24 README.md
-rw-rw-r--  1 user user  1243 Mar 17 10:20 tmux.conf
 ps1_update: command not found
($(cat)user@tiki:~/.vim$ 

And the following is plain terminal output, without tmux running

user@tiki:~$ ls
backup_list.md  Documents  Dropbox   examples.desktop        hakers_and_painters.md~  hyundai     Music     projects  ror  Ubuntu One            Videos          windows.sh
Desktop         Downloads  elif.txt  hakers_and_painters.md  help.txt                 maqola.txt  Pictures  Public    tmp  update_background.sh  VirtualBox VMs
user@tiki:~$ ll
total 116
-rw-rw-r--  1 user user   380 Aug  9 17:34 backup_list.md
drwxr-xr-x  6 user user  4096 Jul 15 09:26 Desktop/
drwxr-xr-x  2 user user  4096 Jul  7 11:26 Documents/
drwxr-xr-x 11 user user 20480 Aug 20 13:53 Downloads/
-rwx------  1 user user   729 May  7 14:45 update_background.sh*
drwxr-xr-x  2 user user  4096 Dec 10  2013 Videos/
drwxrwxr-x  4 user user  4096 Sep 10  2013 VirtualBox VMs/
-rwxrwxr-x  1 user user    36 Jan 11  2014 windows.sh*
user@tiki:~$ cd Desktop/
user@tiki:~/Desktop$ ll
total 36
-rw-rw-r-- 1 user user 3388 Jul 14 17:10 daily--report.md
-rw-rw-r-- 1 user user   71 Jan 28  2014 fernandez readme.md
-rw-rw-r-- 1 user user   23 Jan 28  2014 fernandez readme.md~
drwx------ 4 user user 4096 Mar 23 14:02 my_docs/
drwx------ 2 user user 4096 Feb  3  2014 Origami/
drwx------ 7 user user 4096 Feb  1  2013 Plants_vs._Zombies_v1.2.0.1065/
-rwxr-xr-x 1 user user  301 Apr 15 11:28 Sky Fight.desktop*
drwx------ 2 user user 4096 Feb 11  2014 webdesign/
-rwxrwxr-x 1 user user   26 Jan 11  2014 windows.sh~*
user@tiki:~/Desktop$