I'm not sure of the original question for this post, but I've also had a problem with the "Unresolved" icon not being available, and this post was the only one that came up in Google.
Basically, I'd upgraded from a much older forum, and having done so, most icons had suddenly vanished. The solution was to change the default graphics file extension to "png". This was how I did this:
- Open the "Admin" menu (in the standard DNN way).
- Select "General Settings"
- Expand "Forum User Interface"
- Under "Theme Image Extension", change "gif" to "png".
This solved my problem, and the icons reappeared - as if by magic! May not be relevant to your issue, but hope it's of help to someone.