Wow, it seems that making these changes in the admin.master page solves the problem.
For the clarification, before applying this, I got the error when I tried to navigate on the Administration widget, so yes I saw the Welcome page, I could log in with Admin to the Blog site. But when I tried to access pages like Blogs, Pages, Comments I got the exception.
Could you fix this permanently on the BE source?
I appreciate your help for the suggestions!
Thank you for you time, and your help!
KU