I have the same problems here. Using Hardy Beta upgraded from Gutsy on a HP nx7400 (iwl3945).

Logs:
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) started... 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) scheduled... 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) started... 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) scheduled... 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) complete. 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) starting... 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0/wireless): access point 'portmax' is encrypted, but NO valid key exists.  New key needed. 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) New wireless user key requested for network 'portmax'. 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) complete. 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) New wireless user key for network 'portmax' received. 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) scheduled... 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) started... 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) scheduled... 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) Stage 1 of 5 (Device Prepare) complete. 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0) Stage 2 of 5 (Device Configure) starting... 
Mar 22 11:39:46 nx7400 NetworkManager: <info>  Activation (wlan0/wireless): access point 'portmax' is encrypted, and a key exists.  No new key needed. 
Mar 22 11:39:47 nx7400 NetworkManager: <WARN>  nm_signal_handler(): Caught signal 11.  Generating backtrace... 
Mar 22 11:39:48 nx7400 NetworkManager: ******************* START **********************************
Mar 22 11:39:48 nx7400 NetworkManager: (no debugging symbols found)
Mar 22 11:39:48 nx7400 NetworkManager: Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
Mar 22 11:39:48 nx7400 NetworkManager: (no debugging symbols found)
Mar 22 11:39:48 nx7400 last message repeated 10 times
Mar 22 11:39:48 nx7400 NetworkManager: [Thread debugging using libthread_db enabled]
Mar 22 11:39:48 nx7400 NetworkManager: [New Thread 0xb7b7d720 (LWP 5238)]
Mar 22 11:39:48 nx7400 NetworkManager: [New Thread 0xb737bb90 (LWP 5437)]
Mar 22 11:39:48 nx7400 NetworkManager: [New Thread 0xb7b7cb90 (LWP 5427)]
Mar 22 11:39:48 nx7400 NetworkManager: (no debugging symbols found)
Mar 22 11:39:48 nx7400 last message repeated 9 times
Mar 22 11:39:48 nx7400 NetworkManager: 0xb7f80410 in __kernel_vsyscall ()
Mar 22 11:39:48 nx7400 NetworkManager: ******************* END **********************************



# dpkg -l | grep network-manager
ii  network-manager                            0.6.6-0ubuntu2                network management framework daemon
ii  network-manager-dev                        0.6.6-0ubuntu2                network management framework (development fi
ii  network-manager-gnome                      0.6.6-0ubuntu1                network management framework (GNOME frontend
ii  network-manager-openvpn                    0.3.2svn2342-1ubuntu4         network management framework (OpenVPN plugin

# lspci -vv
10:00.0 Network controller: Intel Corporation PRO/Wireless 3945ABG Network Connection (rev 02)
	Subsystem: Hewlett-Packard Company Compaq 6710b
	Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B-
	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR-
	Latency: 0, Cache Line Size: 64 bytes
	Interrupt: pin A routed to IRQ 219
	Region 0: Memory at f4000000 (32-bit, non-prefetchable) [size=4K]
	Capabilities: [c8] Power Management version 2
		Flags: PMEClk- DSI+ D1- D2- AuxCurrent=0mA PME(D0+,D1-,D2-,D3hot+,D3cold+)
		Status: D0 PME-Enable- DSel=0 DScale=0 PME-
	Capabilities: [d0] Message Signalled Interrupts: Mask- 64bit+ Queue=0/0 Enable+
		Address: 00000000fee0300c  Data: 4132
	Capabilities: [e0] Express Legacy Endpoint IRQ 0
		Device: Supported: MaxPayload 128 bytes, PhantFunc 0, ExtTag-
		Device: Latency L0s <512ns, L1 unlimited
		Device: AtnBtn- AtnInd- PwrInd-
		Device: Errors: Correctable- Non-Fatal- Fatal- Unsupported-
		Device: RlxdOrd+ ExtTag- PhantFunc- AuxPwr- NoSnoop+
		Device: MaxPayload 128 bytes, MaxReadReq 128 bytes
		Link: Supported Speed 2.5Gb/s, Width x1, ASPM L0s L1, Port 0
		Link: Latency L0s <128ns, L1 <64us
		Link: ASPM Disabled RCB 64 bytes CommClk+ ExtSynch-
		Link: Speed 2.5Gb/s, Width x1

# uname -a
Linux nx7400 2.6.24-12-generic #1 SMP Wed Mar 12 23:01:54 UTC 2008 i686 GNU/Linux