Bash script: mal intérprete

Pregunta: me sale este mensaje de error:

exportación: intérprete incorrecto: no existe tal archivo o directorio

cuando ejecuto este script bash:

#!/bin/bash
MONO_PREFIX=/opt/mono-2.6
GNOME_PREFIX=/opt/gnome-2.6
export DYLD_LIBRARY_PATH=$MONO_PREFIX/lib:$DYLD_LIBRARY_PATH
export LD_LIBRARY_PATH=$MONO_PREFIX/lib:$LD_LIBRARY_PATH
export C_INCLUDE_PATH=$MONO_PREFIX/include:$GNOME_PREFIX/include
export ACLOCAL_PATH=$MONO_PREFIX/share/aclocal
export PKG_CONFIG_PATH=$MONO_PREFIX/lib/pkgconfig:$GNOME_PREFIX/lib/pkgconfig
PATH=$MONO_PREFIX/bin:$PATH
PS1="[mono-2.6] \w @ "

Pero el camino bash parece ser correcto:

asshat@IS1300:~/sources/mono-2.6# which bash
/bin/bash

asshat@IS1300:~# cd sources/
asshat@IS1300:~/sources# cd mono-2.6/
asshat@IS1300:~/sources/mono-2.6# ./mono-2.6-environment
export: bad interpreter: No such file or directory
asshat@IS1300:~/sources/mono-2.6# ls
download  mono-2.4  mono-2.4-environment  mono-2.6  mono-2.6-environment
asshat@IS1300:~/sources/mono-2.6# cp mono-2.6-environment mono-2.6-environment.sh
asshat@IS1300:~/sources/mono-2.6# ./mono-2.6-environment.sh
export: bad interpreter: No such file or directory
asshat@IS1300:~/sources/mono-2.6# ls
download  mono-2.4-environment  mono-2.6-environment
mono-2.4  mono-2.6              mono-2.6-environment.sh
asshat@IS1300:~/sources/mono-2.6# bash mono-2.6-environment
asshat@IS1300:~/sources/mono-2.6#

¿Qué estoy haciendo mal? ¿O es un error de Lucid Lynx?

Hice chmod + x