This error is likely to have occurred because the Document is being instructed to show on the Web Kiosk / Web portal.
The setting which controls this is a flag against the Document type of the File in the Documents tab. For example, if your documents are PDF's then:
Click System Admin, Setup, Document Types
Scroll to the document type for PDF's
The option to 'Show on Portal' will be set to Yes
Change this to No to resolve the error
Click Apply.