When updating to v2.1 and you see this error in the console:
Assets/GameDataEditor/Editor/CodeGen/GDECodeGenWindow.cs(7,66): error CS0117: 'GDEManagerWindowBase' does not contain a definition for 'rootMenuLocation'
There are two files you need to delete:
Some code was moved around and those files we renamed and/or removed from GDE v2.1. Delete them and everything will be working again.