If you are playing local files that haven't been scanned into the Kodi library, the add-on may only see a generic filename instead of the metadata required to trigger a search.
The most reliable way to avoid this error is to use streaming add-ons known for providing full metadata to Kodi's subtitle system. Experts on the Diggz Team forums suggest using: Umbrella a4ksubtitles imdb id not provided
For bulk refreshing, use the tool, or simply remove the source and re-add it to your library. If you are playing local files that haven't