Sharepoint Development: "Request failed" with custom page or dlls/assemblies

Note to self - If using any external assemblies that try to access Microsoft.Sharepoint assemblies, remember to change the trust level to full in the web.config.

<trust level="Full" originUrl="" />

This is only used during development.

When it comes to production, install assembly into the GAC with gacutil /i to allow external assemblies access to Microsoft.Sharepoint assemblies.