I have same problem:
jefferson@jeffersonlaptop:~$ sudo iwconfig wlan0 mode ad-hoc Error for wireless request "Set Mode" (8B06) : SET failed on device wlan0 ; Device or resource busy.
jefferson@jeffersonlaptop:~$ uname -a Linux jeffersonlaptop 2.6.24-17-rt #1 SMP PREEMPT RT Thu May 1 16:23:33 UTC 2008 i686 GNU/Linux
jefferson@jeffersonlaptop:~$ dmesg | grep iwl [ 48.377513] iwl3945: Intel(R) PRO/Wireless 3945ABG/BG Network Connection driver for Linux, 1.2.0 [ 48.377523] iwl3945: Copyright(c) 2003-2007 Intel Corporation [ 48.590601] iwl3945: Detected Intel PRO/Wireless 3945ABG Network Connection [ 51.916901] iwl3945: Tunable channels: 13 802.11bg, 23 802.11a channels [ 51.919390] wmaster0: Selected rate control algorithm 'iwl-3945-rs'
I have same problem:
jefferson@ jeffersonlaptop :~$ sudo iwconfig wlan0 mode ad-hoc
Error for wireless request "Set Mode" (8B06) :
SET failed on device wlan0 ; Device or resource busy.
jefferson@ jeffersonlaptop :~$ uname -a
Linux jeffersonlaptop 2.6.24-17-rt #1 SMP PREEMPT RT Thu May 1 16:23:33 UTC 2008 i686 GNU/Linux
jefferson@ jeffersonlaptop :~$ dmesg | grep iwl
[ 48.377513] iwl3945: Intel(R) PRO/Wireless 3945ABG/BG Network Connection driver for Linux, 1.2.0
[ 48.377523] iwl3945: Copyright(c) 2003-2007 Intel Corporation
[ 48.590601] iwl3945: Detected Intel PRO/Wireless 3945ABG Network Connection
[ 51.916901] iwl3945: Tunable channels: 13 802.11bg, 23 802.11a channels
[ 51.919390] wmaster0: Selected rate control algorithm 'iwl-3945-rs'