What it probably means is the attachment point (a.smoke3) that is listed in the config file does not appear in the mesh. How this happened is a bit of a mystery since the automatic checks are set up to catch things like that and reject the upload.
Solutions:
1. The content creator who has the original mesh can correct it by adding the attachment point to the mesh and re-upload a revised version of the item.
2. You can delete that part of the config file concerning a.smoke3 but depending on where it is and what the smoke effect is for it might either look fine or terrible.
Ben