The file you shared is corrupted. Very likely there was a delay in writing to the USB drive. We've seen similar file format problems in the past when files are not locally (internally) saved. It seems to most often happen when saving to the cloud but I've seen it once in awhile when saving to a USB device. The .skb files are backup files that are normally created by SketchUp during autosave. If you can find them you could try renaming them to .skp and see if they will open. If they didn't get corrupted, too, they should open. It's rare that corrupted files can be recovered. Are you using SketchUp 2016 Make as indicated by your profile? Might be the sort of thing where the fastest option is to just get busy creating a new model. This time save it to the local drive and only copy it to the USB drive if you need to make it portable.