I wanna sent email to author of an item. However, I gets error as "Failed to send notification. Cannot get the full name or e-mail address of user". Hence, i copied "Created By" in variable and then used it in "To" box. It shows the same error. Later, I changed its field type to "Login Name". (...) and assigned "To" box to vAuthor variable. see below image.
It shows the same error. Finally, I tried with Email address and then it worked. (see below image)
My query is why "To" box cannot identity "Created By" or People picker control variable directly?
It should work for you when you give directly created by in To field.
Why don't you try to print the Created by value somewhere in share point list or use workflow action "log in history list" to print the value of created by in workflow history.?
This should help you to retrieve what value actually create by is with