Hmm, this is puzzling, especially since you have successfully updated the firmware once before. I can’t think of any obvious reason. The message you encountered means the operating system cannot detect the USBasp device. If you have access to another computer you may want to try it on another computer. Also, I am wondering if this has to do with USB 3.0 (I doubt that, because I have a fairly recent Macbook Air and I can successfully upgrade firmware using it).