E0001: a character that has no place in IEC 61131-3 text

Outside comments, pragmas and string literals, IEC 61131-3 text is made of identifiers, keywords, literals, operators and delimiters (Ed.3 6.1). A character that starts none of them, such as @, ? or !, is an error.

x := a @ b;      (* E0001: '@' *)
x := a + b;      (* fixed *)

Characters other than ASCII are allowed inside comments and string literals only.