Error when Starting Mirror

[Anonymous]

I am doing a Mirror to a Network Drive. I get the Below Error

Error: Please fill all empty directory fields.
(You can ignore the error to consider not existing directories as empty.)

I don't understand what I am doing wrong?

[Zenju]

One of the directories, either source or target, have not been specified, i.e.
the field where the name of the directory is supposed to be placed, is empty.