I am using Window Live Writer for blogger blog.It is a wonderful tool and it has lot of features. And When i started using this i could see there is a problem in split post option(Read More Option) and it is not at all enabled(Grayed out).Now i solved this problem with below techniques.
If you have a same problem following steps will help you to solve this problem.
Step1 :-
1.Download the plug-in InsertBloggerExcerpt.dll from below location
Download here
Step2 :-
2.
Copy the plugin to this location
C:Program FilesWindows Live WriterPlugins
Step3:-
3. Close and open your windows live writer.
Step4:
4.Check it is there
Step5:
In your post click where your want Read More link.