If you are getting below error when you have deployed your web application which connects to Microsoft Dynamics CRM 2011 online/on premise version.
Could not load file or assembly ‘microsoft.crm.sdk.proxy’ or one of its dependencies. This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded.
Then probably you have used wrong IIS Application Pool. You might want to change the .Net version of assigned Application Pool to 4.0. And re-run the site.
This should solve the error you were facing.