The destination folder specified is invalid in Appian v18.1

Hi all,

I ran into the problem of "The destination folder specified is invalid." while I was uploading a document.

a!formLayout(
  contents:{
    a!fileUploadField(
label: "Upload a File"&ri!document,
labelPosition: "ABOVE",
target:cons!COM_FOLDER_TEMP_DOCS,
value: ri!document,
saveInto: ri!document,
validations: {}
)
  },
buttons: a!buttonLayout(
primaryButtons: a!buttonWidgetSubmit(
label:"Submit",
style: "PRIMARY"
)
),
validations:{
}
)

I have checked the security of the constant, the folder in the constant and the KC containing the folder , and I have confirmed that the user has already given the right to access the folder.

Actually, I have found an error regarding to my Default Community, I wonder that has led in the problem above, but I was unable to update the security at all.

Do you have any clues?