Peripherals: files won't copy invalid ms-dos function

files won't copy invalid ms-dos function

I regularly back up my data files to an external hard drive. Went to do my back up yesterday and wouldn't copy any file to an external media, not to external hard drive, not to disk and not to a flash card. I've been backing up this stuff for quite a while and don't understand why all of a sudden there is a problem. I'm mainly copying embroidery design files which aren't very big. But it wouldn't copy office files etc. The only think I could get it to write to was a flash card through an embroidery progam I have where among other things you can write to external cards through. That works ok. But I back up 50k+ embroidery files that way. Oh running Vista. TIA for any help