Failed to open form in b1 client. C# add-on

Hi, experts.

I have an error when I try to open a form in b1 client.

The error is shown on screen:

using System; using System.Collections.Generic; using System.Text; using SAPbouiCOM.Framework; using SAPbouiCOM; namespace WarningsProject {     class Menu     {         private SAPbouiCOM.Application UIApp = SAPbouiCOM.Framework.Application.SBO_Application;                 public void SBO_Application_MenuEvent(ref SAPbouiCOM.MenuEvent pVal, out bool BubbleEvent)         {             BubbleEvent = true;             try             {                 ContextMenu contextMenu = ContextMenu.GetObj;                 if ( pVal.BeforeAction )                 {                     if ( pVal.MenuUID == "3591" )                     {                         contextMenu.Clear();                         contextMenu.CreateMenu(string.Format("Учет запчастей/расходников и краски"));                     }                     if (pVal.MenuUID == "subMenu0")                     {                         var f = new UDOForm2();                     }                 }                             }             catch (Exception ex)             {                 SAPbouiCOM.Framework.Application.SBO_Application.MessageBox(ex.ToString(), 1, "Ok", "", "");             }         }     } } using System; using System.Collections.Generic; using System.Linq; using System.Text; using SAPbouiCOM.Framework; namespace WarningsProject {     [FormAttribute("UDO_FT_warning_udo")]     class UDOForm2 : UserFormBase     {         private SAPbouiCOM.Application UIApp = SAPbouiCOM.Framework.Application.SBO_Application;                 public UDOForm2()         {                 }         public override void OnInitializeComponent()         {             this.OnCustomInitialize();         }         private void OnCustomInitialize()         {         }     } }