My expertise on this subject is so minimal as to be nonexistant, but I think you might be wise to ignore the "usb device not supported" message. I get this message every time I switch to host mode, using USB Control, whether a device is connected or not. And while some devices don't work, others do, despite the warning.

The N810 does seem to be very picky about which flash drives it will deal with. Some work, some don't, but all are greeted with the "usb device not supported" message.

Please note, this is just my experience, and not necessarily what others have experienced. I am NOT claiming that you don't have a problem, only that the "device not supported" message may be irrelevant to diagnosing and correcting the problem.

No worries RobbH, I used to get that all the time when it was working, this is because there is a list of devices that the tablet "officially supports" and so it shows this error even though the device works. But as of a few days ago I've had a problem where as soon as I switch to host mode before I have plugged anything in I immediately get a usb device not supported error pop up once as if there is some phantom device plugged in, then when I do plug in the usb device (ive tried loads of devices that used to work before: multiple flash drives, usb keyboards even my mobile phone) nothing happens at all, the usb device gets no power whatsoever so my tablet never realises its there. I have a feeling that for some reason or other the usb controller is unable to raise the voltage of the port to the requisite 5 volts in order to power the device because whenever I switch to host mode it always says in dmesg that there was an error in a_wait_vrise and that the vbus is too slow.

I tried reflashing my n810 with an older chinook firmware 1.2007.42-18 and I still have exactly the same problem where I can't get any usb device to work. I'm starting to think that this is a hardware problem.

Do you think I should just return my n810 for a replacement and be done with it?