Setting master mode fails

Hi,

I want to put up an access point. Performing »iwconfig wlan0 mode master«
complains:

Error for wireless request "Set Mode" (8B06) :
SET failed on device wlan0 ; Invalid argument

kernel 2.6.32-2-686

lsusb:
Bus 001 Device 002: ID 148f:2573 Ralink Technology, Corp. RT2501USB
Wireless Adapter

moduls:
rt2500usb, rt73usb, rt2x00usb, rt2x00lib

iwconfig:
wlan0 IEEE 802.11bg ESSID:"test"
Mode:Managed Frequency:2.422 GHz Access Point: Not-Associated
[...]

What's the problem?

Marco

I solved it, using hostapd. But I still have problems. I open a new thread.