X64 ASP.net failing to find assembly

I am having an issue with something that seems like it should be simple. I am just trying to use the sharepoint object model from an ASP.net page. It's running on Framework 3.5 (required by sharepoint), and I realize it needs to be set to build on x64 (also required by sharepoint from what I understand). The issue is when I do this it returns "Could not load file or assemply ". If I switch it to any CPU then it reports that the call to build SPSite can't find the site address.

Basically if I open a brand new web ap开发者_StackOverflow中文版p project and switch it to framework 3.5 and build target x64 it will report this same error. It seems like I am doing something stupid but I have no idea what it could be.

Ensure your IIS AppPool is set to x64.

The DLL's project build output / platform should be set to Any CPU.