The Appian folder names cannot contain any of the following characters: \\ / ; :

1) this is an ancient thread

2) if you merely want to get rid of the characters in question (not replace with underscores, though if so you might prefer Robert's posted code), i have a rule set up in my system i.e. "rule!ASDF_RULE_SanitizeFilename()" which i pass all new file or folder names through, that does this:

stripwith(
  ri!fileName,
  
  /*
    The following constant contains this string:
    \/;:"|?'><*
  */
  cons!ASDF_TEXT_INVALID_DOC_FLDR_CHARACTERS
)