Please make sure you are downloading onto your computer and unzipping it on your computer before you transfer it onto your phone downloading onto your phone and or unzipping on your phone will cause issues in some cases.
Also please make sure you are not renaming the files. Technically you can rename the files but there are certain characters you cannot use without causing the file to fail the md5 check. Best thing you can do is just not rename it.
Barring these two things the main issue you may be having is just getting a bad download or transfer when moving it to your phone. If either of the two above things do not work then redownload it and retransfer it.
“All is caprice, they love without measure those whom they will soon hate without reason.”—Thomas Sydenham