If you have already worked around the installation issue and are using XNA Game Studio on Windows 8, you might notice warnings when opening or building content projects. The warnings look like the following: C:WindowsMicrosoft.NETFrameworkv4.0.30319Microsoft.Common.targets(1546,5): warning MSB3270: There was a mismatch between the processor architecture of the project being built "MSIL" and the processor architecture of the reference "Microsoft.Xna.Framework.Content.Pipeline.AudioImporters, Version=4.0.0.0, Culture=neutral, PublicKeyToken=842cf8be1de50553, processorArchitecture=MSIL", "x86". This mismatch may cause runtime failures. Please consider changing the targeted processor architecture of your project through the Configuration Manager so as to align the processor architectures between your project and references, or take a dependency on references with a processor architecture that matches the targeted processor architecture of your project
Excerpt from:
How to work around XNA Game Studio content pipeline warnings that can appear on Windows 8