Error 10 (FCDD_SIZE_LJ) indicates that one or more of the HID USB device paths are too large for the 256 byte/character buffer. Basically what is going on is the library is searching the system for HID USB devices to find U12s. As it goes through the list of them, it tries to open each one to get some info about it to see if it is a U12. There is a device path associated with each device, which is what is used to open it. There is a check in the library to see how big that device path is, so that it doesn't overflow the buffer. If the device path is too large, it sets an error code, then skips that device and moves on.
So the function still works when it returns error 10, but it just sets an error to let the user know that one or more might of been skipped. U12 device paths should be under the device path buffer limit and more than likely this error is caused by other HID USB devices when it goes through HID list.