NGUI Free import problems

[Wasabi]

Good day NGUI Community
I wanted to try NGUI in one of my Projects before I buy it.
In an Empty Project it is Working fine and all Examples working grate, but if I Import the Free Package in my existing Unity Project I get Tons of errors like these:

1. Assets/NGUI/Scripts/Editor/UIDrawCallInspector.cs(20,30): error CS0115: `UIDrawCallInspector.OnInspectorGUI()' is marked as an override but no suitable method found to override
2. Assets/NGUI/Scripts/Editor/UIWidgetInspector.cs(35,30): error CS0115: `UIWidgetInspector.OnInspectorGUI()' is marked as an override but no suitable method found to override
3. Assets/NGUI/Scripts/Editor/UIFontInspector.cs(73,30): error CS0115: `UIFontInspector.OnInspectorGUI()' is marked as an override but no suitable method found to override
4.  

If its relevant I also Use ex2D and PieMenu in that Project.
Any Idea what could be the Problem?

Greetings
Wasi

[Wasabi]

Sorry, My Bad 

I had a Costum Class Named Editor.
I didn't thougth of that it could be conflict with the UnityEditor.Editor Class.

Any Warning from Unity would be nice.