I have been experiencing this problem for more than a year now and everything I've tried does not work.
I have an Acer Aspire 5551 laptop running Windows 7 Home Basic. I think it's about 5 years old now. I cannot copy ANY files (really, none at all) from my laptop to my external hard drive (Prestige Desktop Hard Drive Hi-Speed USB 2.0). I used to be able to, but then one day it decided to reject them, giving me the "Cannot read from source file or disk" message. Now today I tried to copy one .avi file of 349 MB from my laptop to the external and it actually worked, so I tried to copy another .avi file of the same size but then it just gave me that message again.
I can still copy files from my external to my laptop and I used to be able to copy files to the external with other computers and laptops but now it won't work on any of them either.
I would really appreciate the help!