This is not the proper syntax ...
$validate(something,blah,blah)
See Mp3tag Help Manual.
The function $validate(filename,to) replaces all invalid characters, regarding the creation of filepathnames, with one dedicated character, chosen by the user.
Some invalid characters are: /?*"<>|:
Example: $validate(%ARTIST%' - '%ALBUM%' - '%TRACK%' - '%TITLE%,'_')
Example: $validate(%ARTIST%' - '%ALBUM%' - '%TRACK%' - '%TITLE%,)
DD.20150202.2009.CET
See also ...
[F] $validate() broken?
Character remapping during conversion?
DD.20150202.2039.CET