WSS 3.0 lost permissions

I have a standard list of announcements in a Sharepoint services site where each item has it’s own permissions based on it’s audience. Yesterday I started getting calls saying users couldn’t see the announcements pertaining to them. I went in as admin and found that most of the items now have no permissions.

Any thoughts on how to troubleshoot this? Only 3 of us have full control of this list and we can’t figure out if we did anything to cause the loss of permissions.

Any help would be appreciated.