What Does 'Xvidcore.dll Is Not Found' in Windows Mean?

Symptoms
The 'Xvidcore.dll is not found' error message usually appears on the screen when you try to load a video that relies on the Xvid codec, a program that decodes and compresses video. The codec is primarily used for playing media files in formats such as MPEG-4. Certain media programs and websites will not play videos without the codec.
Causes
The 'Xvidcore.dll is not found' message appears if the Xvid codec is missing, damaged or corrupt. It may also appear if it isn't installed. When you load a video encoded using Xvid, a media player such as Windows Media Player prompts you to download and install the codec. If the codec was previously installed, accidentally deleting the file or registry issues also cause errors when you try to play Xvid movies.
Solution
If you're unable to play Xvid encoded movies, download and install the latest version of the Xvid codec. When you download the codec, follow the guided prompts to install it into the correct folder or the error message will continue to pop up when you load Xvid encoded movies. After installing the codec, you must restart your media program for the changes to take effect. If you were trying to watch an Xvid encoded video on the Internet, restart your browser for the changes to take effect.
Tips
In some cases, issues with the Xvidcore.dll file may be as a result of malware such as Trojans and spyware. These programs secretly install on the computer, modify registry entries and cause problems that can interfere with the Xvid codec, especially when you to watch online videos. Run anti-virus and anti-spyware scans to remove problem-causing malware.