When I find situations like these, I post a comment to alert the user to create a real answer and mark it as accepted once the allotted time has passed. It also wouldn't hurt to explain why it should be an answer instead of a comment (benefits to the site, future visitors, etc).
I find that most of the time, letting the user know to answer/mark accepted that they will follow through, assuming they come back to the site.
Example: Internal Server Error - Downloading attachmentsInternal Server Error - Downloading attachments