FTDI usb-serial adapter does not work anymore

I use FTDI usb-serial adapter to interact with few devices here. Some time ago I rebooted my home machine and noticed that my dongle stopped working:

13:21 hrw@home:~$ sudo picocom -b115200 /dev/ttyUSB0
picocom v1.4

port is : /dev/ttyUSB0
flowcontrol : none
baudrate is : 115200
parity is : none
databits are : 8
escape is : C-a
noinit is : no
noreset is : no
nolock is : no
send_cmd is : ascii_xfr -s -v -l10
receive_cmd is : rz -vv

FATAL: cannot open /dev/ttyUSB0: Resource temporarily unavailable

I upgrade kernel packages when they are released but reboot just once per few weeks so it is hard to check which kernel release stopped working. Checked with Ubuntu mainline kernel packages - vmlinuz-2.6.37-020637rc5-generic is the one where my adapter works properly with same picocom call (works for root and normal user).

13:18 hrw@home:~$ uname -a
Linux home 2.6.37-8-generic #21-Ubuntu SMP Sun Dec 5 17:56:47 UTC 2010 x86_64 GNU/Linux
13:18 hrw@home:~$ cat /proc/version_signature
Ubuntu 2.6.37-8.21-generic 2.6.37-rc4

Problematic device is:

Bus 002 Device 004: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC
Device Descriptor:
  bLength 18
  bDescriptorType 1
  bcdUSB 1.10
  bDeviceClass 0 (Defined at Interface level)
  bDeviceSubClass 0
  bDeviceProtocol 0
  bMaxPacketSize0 8
  idVendor 0x0403 Future Technology Devices International, Ltd
  idProduct 0x6001 FT232 USB-Serial (UART) IC
  bcdDevice 4.00
  iManufacturer 1 ftdi
  iProduct 2 usb serial converter
  iSerial 3 ftDIF64Y
  bNumConfigurations 1
  Configuration Descriptor:
    bLength 9
    bDescriptorType 2
    wTotalLength 32
    bNumInterfaces 1
    bConfigurationValue 1
    iConfiguration 0
    bmAttributes 0xa0
      (Bus Powered)
      Remote Wakeup
    MaxPower 44mA
    Interface Descriptor:
      bLength 9
      bDescriptorType 4
      bInterfaceNumber 0
      bAlternateSetting 0
      bNumEndpoints 2
      bInterfaceClass 255 Vendor Specific Class
      bInterfaceSubClass 255 Vendor Specific Subclass
      bInterfaceProtocol 255 Vendor Specific Protocol
      iInterface 2 usb serial converter
      Endpoint Descriptor:
        bLength 7
        bDescriptorType 5
        bEndpointAddress 0x81 EP 1 IN
        bmAttributes 2
          Transfer Type Bulk
          Synch Type None
          Usage Type Data
        wMaxPacketSize 0x0040 1x 64 bytes
        bInterval 0
      Endpoint Descriptor:
        bLength 7
        bDescriptorType 5
        bEndpointAddress 0x02 EP 2 OUT
        bmAttributes 2
          Transfer Type Bulk
          Synch Type None
          Usage Type Data
        wMaxPacketSize 0x0040 1x 64 bytes
        bInterval 0
Device Status: 0x0000
  (Bus Powered)

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: linux-image-2.6.37-8-generic 2.6.37-8.21
Regression: Yes
ProcVersionSignature: Ubuntu 2.6.37-8.21-generic 2.6.37-rc4
Uname: Linux 2.6.37-8-generic x86_64
Architecture: amd64
Date: Mon Dec 13 13:16:39 2010
InstallationMedia: Kubuntu 10.04 "Lucid Lynx" - Release Candidate amd64 (20100419.1)
ProcEnviron:
 SHELL=/bin/bash
 LANG=pl_PL.UTF-8
 LANGUAGE=
SourcePackage: linux