var ps = new PermissionSet(PermissionState.None);
ps.AddPermission(new SecurityPermission(SecurityPermissionFlag.BindingRedirects |
                                        SecurityPermissionFlag.Execution |
                                        SecurityPermissionFlag.Infrastructure | SecurityPermissionFlag.Assertion
                                        | SecurityPermissionFlag.ControlThread));
ps.AddPermission(new FileIOPermission(FileIOPermissionAccess.AllAccess, pluginPath));
ps.SetPermission(new ReflectionPermission(PermissionState.Unrestricted));

domain = AppDomain.CreateDomain(appDomainName, AppDomain.CurrentDomain.Evidence, setup, ps,strongNames);

var pluginLoaderObj = Activator.CreateInstanceFrom(domain,
    parameters.PathToMainAssembly,
    parameters.MainClass);

plugin = (TPlagin) pluginLoaderObj.Unwrap();
plugin.CallMethod("MethodName"); //тут работает рефлексия