If you get an error specifically for part04.rar , ensure the file is in the same folder as all other parts and has the exact same naming convention.
Once extracted, run the resulting .exe or copy the files into your program's installation directory. Troubleshooting Common Issues Download Patch part04 rar
Check that all parts (except the final one) are the same size. A different size often indicates a corrupt download that needs to be redownloaded. If you get an error specifically for part04