CRC32, MD5 and SHA-1 are hashes, and are supposed to work somewhat like unique identifiers of a file. If your file has an MD5 of 60cf85acc9e07f6c4ab07645acc936fb and your friend's file has an MD5 of 60cf85acc9e07f6c4ab07645acc936fb, you can be (almost) sure you have the same file without needing to actually send the files to each other. There are databases online where you can look up the correct hashes for games. (Do not trust them when it comes to WAD files, though. All good WAD dumps of titles downloaded from the Wii Shop Channel are unique per console, so if you have a good dump, it's pretty much guaranteed that it will not match whatever hashes you can find online. The databases are very useful for disc games, though.)
And yeah, those two reported problems are extremely common for WAD files (even though I would like them not to be...)
And yeah, those two reported problems are extremely common for WAD files (even though I would like them not to be...)