I had the same problem with my USB Archos 43 Vision.
The problem is the new Debian testing Linux kernel : 2.6.38
I tried with the Liquorix kernel (a 2.6.38 !) and it didn't work too.
I found two solutions (merci Google !) :
1- upgrade to kernel 2.6.39, it means using part of Sid packages instead Testing
2 - to fix the problem directly in the kernel 2.6.38 sources with usb-storage and recompile it...
I choosed the second solution.
, I have to patch the file /drivers/scsi/sd.c in Linux kernel sources
Now it works perfectly, it was a long time ago I haven't to recompile a linux kernel !
Hope I help you