New Post: Error message "A IDockManager extension must be included..." after upgrading to version 1.7

More info: I tried with creating an empty class put in a separate project, built it and put the DLL put in the Plugins folder, but the problem remains. I also tried putting it as

Some observations:
-After appManager.LoadExtensions() is called, the folder "Windows Extensions" is added to the appManager.Directories list. I have no Windows Extension folder in my output directory.
-In the DS 1.7 download package, there is no DotSpatial.Plugins.TabbedDocking.dll in folder Windows Extensions (it was in version 1.6).