There is possibly a simple text error in the redirection address or you have used different lower case and capital letters in the redirection address to those used in the folder name.
Please ensure that the address you entered is identical to the folder name address.
When you enter a "Subfolder" in the redirection address the folder must also begin with a capitalised "S", otherwise you will be redirected but in the browser, the error message you described appears.

This is because we are operating with the Unix system, which treats capital and lower case letters as different characters.