I'd have to say a lot of the problems I've seen in this thread have the same resolutions. If you have anything to add, feel free!
Look for your problem description and try out the solution before posting.
File Corruption Messages from a Player
Verify the file by calculating a checksum. You can typically find the checksum in the filename.
I'll use Naruto as an example.
Here's the file name: [AonE]_Naruto_98_[<u>6915F004</u>].avi
The checksum is underlined. Calculate the checksum of the file using something like hkSFV. hkSFV will generate a checksum file with an entry like this:
[AonE]_Naruto_98_[6915F004].avi 6915f004
Notice how the bold strings match. This shows that the file you received most likely works*.
If it doesn't match, you'll probably have to redownload the file.
For you BitTorrent users out there, you can be doubly sure that your file works because BitTorrent automatically verifies your file as it downloads it in chunks.
You can download hkSFV at http://www.big-o-software.com/products/hksfv/
* Barring CRC32 collisions, of course. However, for our purposes, this mostly likely won't happen.
Anime Viewing Problems (Can't Open, Artifacts on Screen, Dies in Middle)
Refer to File Corruption Above first, then proceed.
Most likely, you have a codec problem. Depending on the anime, you'll need DivX or XviD to view it.
You can grab DivX from http://www.divx.com/.
The XviD folks don't provide binaries. You'll need to find someone who provides them. I recommend Koepi's binaries because of the generally good build quality and inclusion of some handy tools.
Grab Koepi's XviD Binaries from http://www.koepi.org/
For you folks with the artifacts appearing or mid-show crashes, I emphasize that you must get the latest codecs. (Example: The later episodes of Naruto don't play too well with XviD versions prior to 1.0. Upgrading to 1.0 fixes this)
A note on Codec Packs
I don't recommend using a codec pack due to problems I have had using them (namely, Nimo's Codec Pack).
I do recommend, however, downloading the individual codecs yourself and installing them separately.
You will most likely have to uninstall what the codec pack installed to clean everything up first.
Okay, my codecs and checksums are fine
Then you probably have other problems on your computer. Do other applications act abnormally?
Take a dose of
AdAware (http://www.lavasoftusa.com/)
and your favorite AntiVirus.
I think I'll leave it at that for now.