I received this error after getting a copy of a .Net 4 web-site out of our source repository that uses ODP.Net to connect to Oracle. The setup I have puts all of the required Oracle binaries into the ASP.NET bin directory so it’s easily portable. Here was my gotcha. There is one Oracle assembly (oraociei11.dll) that is 127MB and currently is too large to check into our source repository. I quickly remembered this, obtained the assembly from the location I’d referenced in my notes that I should have read, put it in the Bin directory and rebuilt the site. Problem solved.