I have a problem with Visual Studio 2010 and Outlook Addin 2010 project (.NET 4 target). I ve added a form region to my project and then I ve changed Localizable property to true. Now if I close my form region and reopen it, I m getting this VS error page:

To prevent possible data loss before loading the designer, the following errors 
must be resolved: 
The variable  resources  is either undeclared or was never assigned.

This actually happens when I change any property in Form Region or Ribbon if the code is targeted for .NET 4. In projects targeted for .NET 3.5 everything is in order. Here s the example code that this error refers to was created by VS and it s a part of FormRegion.Designer.cs. It breaks on ApplyResources line (if I comment it out then everything is ok).

private void InitializeComponent()
{
    System.ComponentModel.ComponentResourceManager resources = 
        new System.ComponentModel.ComponentResourceManager(typeof(FormRegion1));
    this.SuspendLayout();
    // 
    // FormRegion1
    // 
    resources.ApplyResources(this, "$this");
    this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
    this.Name = "FormRegion1";
    this.FormRegionShowing += 
        new System.EventHandler(this.FormRegion1_FormRegionShowing);
    this.FormRegionClosed += 
        new System.EventHandler(this.FormRegion1_FormRegionClosed);
    this.ResumeLayout(false);
}

If I choose to ignore the error and force VS to load visual editor then I m getting another error:

Cannot open a designer for the file because the class within it does not inherit 
from a class that can be visually designed. 

At first I though it s a problem with my code (I have my project migrated from VS2008 and Outlook 2007). But then I created a new project for VS2010 and Outlook 2010 and I have the same problem there.

Steps to reproduce it:

1. Create a new Outlook 2010 Addin project in Visual Studio 2010 (.NET 4)
2. Add a new FormRegion item to a project (it doesn t matter for which item you enables it, it also doesn t matter if it s adjoined or separate form region)
3. Open new item properties and change Localizable property to true
4. Close item and reopen it