I would recommend enabling debug mode in web.config file as described in the error page to see more details. Also, if you are using any custom event handlers, custom macro methods or anything which is registered as a class in App_Code or custom assembly project, make sure they are registered using unique names in the constructors. I mean this in the class code:
// Module class constructor, the system registers the module under the name "CustomInit"
Maybe you have more modules with the same constructor name.