[Rufus]

Are you paying attention to where you are trying to save it at?

i.e. -
What folder, in what location and in what format? You may have something totally off the wall defaulted in your "Save As.." screen.

Maybe reply with screenshots, or your set-up in the "Save As" screen, or you might just solve your own problem by taking a closer look at that.

Do you have a storage card? Maybe try changing your location to or from the Storage Card, just to see if you can save at all.