PyUSB

Fixed on revision 1.26.
All return calls were fixed, and I also added defensive code by checking
against "No Error" messages. Thank you for the help.

Talking to the libusb maintainer resulted in the following statement:

-----------------------------------------------------------------------------------
It [the error] comes from libusb because pyusb calls usb_strerror() when
there is no
error. Quoting the libusb Developers Guide:

| Chapter 7. Return values
| There are two types of return values used in libusb v0.1. The first
| is a handle returned by usb_open. The second is an int. In all cases
| where an int is returned, >= 0 is a success and < 0 is an error
| condition.

On the other side pyusb checks for a value != 0, so it thinks some
returned values are error while they are not.
------------------------------------------------------------------------------

No, it hasn't.

I came across the same problem with a different device and I have a
question:
Has this been forwarded as a bug to libusb guys?

With kind regards,
Marek

Then I'd suggest to return something like 'No errormessage', so it is
obvious to the User. Just 'No error' is confusing, definitely.

PyUSB just replicates the error reported by the underline libusb library.
This is caused because a libusb function has returned with error but hasn't
set a error message.