I have tried both successfully and unsuccessfully to delete the Downloads folder, and/or temp files when getting this error.
I have found that when deleting doesn't work, renaming the Downloads folder does. That is, I *rename the Downloads folder to DownloadsX or something like that*. I am not sure why this works, I guess it has something to do with not making the space occupied by the bad files (perhaps bad blocks?) available and forcing new blocks of space to be used when downloading again and creating the temp files.
Try this! After days of frustration trying everything else, this subtle difference worked for me.