usb-to-serial converter problem

Hi, all.

I have a strange problem with my usb-to-serial converter TU-S9
(http://www.trendnet.com/products/proddetail.asp?prod=265_TU-S9&cat=32). When i attach it, i see /dev/ttyUSB0 device, but i cann't communicate with a switch console from minicom. minicom show nothing, just like no switch at all on another side of TU-S9. On my old notebook dell inspiron 1501 it worked fine, on another machine it works fine, but on my new dell inspiron n5110 it doesn't work correctly.
Now I'm using Debian 6, vanilla kernel 3.2.14. When TU-S9 is connected, dmesg
show:

usb 3-2: new full-speed USB device number 3 using xhci_hcd xhci_hcd 0000:0b:00.0: WARN: short transfer on control ep xhci_hcd 0000:0b:00.0: WARN: short transfer on control ep xhci_hcd 0000:0b:00.0: WARN: short transfer on control ep pl2303 3-2:1.0: pl2303 converter detected
usb 3-2: pl2303 converter now attached to ttyUSB0

What i do wrong?
May be the problem exist bacause of inspiron n5110 have no usb 1.1 host?

Thanks.