Finder Copy errors

Im trying to backup an external hd to another external hd.

they are both fw, and daisychained.

im gettting error code 36 (which is an I/O error, http://macs.about.com/gi/dynamic/of.../docs.info.apple.com/article.html?artnum=9805)

what am i supposed todo? they are just random files, like one was a text file it errored out on. it seems to be a different file each time, but they have repeated as well

i should also add this.

i tried to copy files from source external to my internal, all went well. i then tried to copy from internal to my 2nd external hd....same result as a direct ext hd to ext hd copy