A bit of refactoring to be able to find some issue...

GreenshotPlugin/Interfaces/Plugin/HotKeyHandler.cs

@@ -1,4 +1,4 @@
-namespace Greenshot.Plugin
+namespace GreenshotPlugin.Interfaces.Plugin
 {
     public delegate void HotKeyHandler();
 }

GreenshotPlugin/Interfaces/Plugin/IGreenshotHost.cs

@@ -1,6 +1,6 @@
 using System.Drawing;
 
-namespace Greenshot.Plugin
+namespace GreenshotPlugin.Interfaces.Plugin
 {
     /// <summary>
     /// This interface is the GreenshotPluginHost, that which "Hosts" the plugin.

GreenshotPlugin/Interfaces/Plugin/IGreenshotPlugin.cs

@@ -1,6 +1,6 @@
 using System;
 
-namespace Greenshot.Plugin
+namespace GreenshotPlugin.Interfaces.Plugin
 {
     /// <summary>
     /// This defines the plugin

GreenshotPlugin/Interfaces/Plugin/PluginAttribute.cs

@@ -21,7 +21,7 @@
 
 using System;
 
-namespace Greenshot.Plugin {
+namespace GreenshotPlugin.Interfaces.Plugin {
 	[Serializable]
 	[AttributeUsage(AttributeTargets.Class, Inherited = false, AllowMultiple = false)]
 	public sealed class PluginAttribute : Attribute, IComparable {

GreenshotPlugin/Interfaces/Plugin/SurfaceOutputSettings.cs

@@ -1,9 +1,9 @@
 using System.Collections.Generic;
-using Greenshot.IniFile;
 using GreenshotPlugin.Core;
 using GreenshotPlugin.Effects;
+using GreenshotPlugin.IniFile;
 
-namespace Greenshot.Plugin
+namespace GreenshotPlugin.Interfaces.Plugin
 {
     public class SurfaceOutputSettings {
         private static readonly CoreConfiguration CoreConfig = IniConfig.GetIniSection<CoreConfiguration>();