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?