Really need help

It should be the namespace at the top of the PaysonPaymentController file.

hmm I get the same error anyway.

I add all my code.

namespace Nop.Plugin.Payments.Payson
{
    public partial class RouteProvider : IRouteProvider
    {
        public void RegisterRoutes(RouteCollection routes)
        {
            routes.MapRoute("Plugin.Payments.Payson.Configure",
                 "Plugins/PaysonPayment/Configure",
                 new { controller = "PaysonPayment", action = "Configure" },
                 new[] { "Nop.Plugin.Payments.Payson.Controllers" }
            );

            routes.MapRoute("Plugin.Payments.Payson.PaymentInfo",
                "Plugins/PaysonPayment/PaymentInfo",
                new { controller = "PaysonPayment", action = "PaymentInfo" },
                new[] { "Nop.Plugin.Payments.Payson.Controllers" }
           );
        }

        public int Priority
        {
            get
            {
                return 0;
            }
        }
    }
}

namespace Nop.Plugin.Payments.Payson.Controllers
{
    class PaysonPaymentController : BaseNopPaymentController
    {
.......
[AdminAuthorize]
    [ChildActionOnly]
    public ActionResult Configure()
    {
        var model = new ConfigurationModel();
        model.UseSandbox = _paysonPaymentSettings.UseSandBox;
        model.AgentId = _paysonPaymentSettings.AgentId;
        model.CancelUrl = _paysonPaymentSettings.CancelUrl;
        model.SellerEmail = _paysonPaymentSettings.SellerEmail;
        model.Description = _paysonPaymentSettings.Description;
        model.OkUrl = _paysonPaymentSettings.OkUrl;
        model.Md5 = _paysonPaymentSettings.Md5;
        model.GuaranteeOffered = _paysonPaymentSettings.GuaranteeOffered;

        return View("Nop.Plugin.Payments.Payson.Views.PaymentPaysonStandard.Configure", model);
    }

    [HttpPost]
    [AdminAuthorize]
    [ChildActionOnly]
    public ActionResult Configure(ConfigurationModel model)
    {
        if (!ModelState.IsValid)
            return Configure();

        _paysonPaymentSettings.UseSandBox = model.UseSandbox;
        _paysonPaymentSettings.AgentId = model.AgentId;
        _paysonPaymentSettings.CancelUrl = model.CancelUrl;
        _paysonPaymentSettings.SellerEmail = model.SellerEmail;
        _paysonPaymentSettings.Description = model.Description;
        _paysonPaymentSettings.OkUrl = model.OkUrl;
        _paysonPaymentSettings.Md5 = model.Md5;
        _paysonPaymentSettings.GuaranteeOffered = model.GuaranteeOffered;

        return View("Nop.Plugin.Payments.Payson.Views.PaymentPaysonStandard.Configure", model);
    }

namespace Nop.Plugin.Payments.Payson
{
    public class PaymentProcessor : BasePlugin, IPaymentMethod
    {
.....
public void GetConfigurationRoute(out string actionName, out string controllerName, out RouteValueDictionary routeValues)
        {
            actionName = "Configure";
            controllerName = "PaysonPayment";
            routeValues = new RouteValueDictionary() { { "Namespaces", "Nop.Plugin.Payments.Payson.Controllers" }, { "area", null } };
        }

        public void GetPaymentInfoRoute(out string actionName, out string controllerName, out RouteValueDictionary routeValues)
        {
            actionName = "PaymentInfo";
            controllerName = "PaysonPayment";
            routeValues = new RouteValueDictionary() { { "Namespaces", "Nop.Plugin.Payments.Payson.Controllers" }, { "area", null } };
        }

That all looks right from what I can tell.

If you put a breakpoint in GetConfigurationRoute, does it get hit?

Another thing to check, is your Output path in the project settings set to ..\..\Presentation\Nop.Web\Plugins\PLUGINNAME\

I think I'll give up :(

My output is "..\..\Presentation\Nop.Web\Plugins\Payment.Payson\"

It will not get a hit, debug stops on the row "    @Html.Action(Model.ConfigurationActionName, Model.ConfigurationControllerName, Model.ConfigurationRouteValues);" in ConfigurationMethod.cs.

Uninstall the plugin and reinstall it.  Is your Description.txt correct?

Thank you for all your help :)

My Description looks like this:
Group: Payment methods
FriendlyName: Payson
SystemName: Payments.Payson
Version: 1.0
SupportedVersions: 2.40
Author: Magnus Hallberg
DisplayOrder: 1
FileName: Nop.Plugin.Payments.Payson.dll

I have uninstall it and install it again and I get the same error.

Could you share your plugin project?

I can share it, how do I do? I do not have space so I can upload it

Is it possible to build a payment method without using nop classes?