usb_modeswitch not working; lsusb indicate "unable to initialize libusb: -99"; howto?

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http://www.linuxquestions.org – Hello, by connecting a usb gsm modem on a selfbuild kernel, the usb is recognized because dmesg show messages like "New USB device found, idVendor=0af0, idProduct=7a01.." but usb_modeswitch say "No devices in default mode found.." and the modem is not modeswitched. The command lsusb gives "unable to initialize libusb: -99". A question would be: is there any possibility to modeswitch a usb modem (a standard distro like ubuntu-kernel see a CD-ROM.. and usb_modeswitch works) which is not recognized as CDROM by the kernel? My current feeling is that I have to build a (HowTos)