I think we experienced something like this a while back. Try to move the documents to another folder. Remove the orignal folder, create a new with the same name and correct access right and then move the files back.
I think we did something like the above.
I have a mysterious problem:
One of the folders under Global is no longer accessible for everyone, even though Everyone has read rights in the file handler. The unauthorized user gets the EPiServer login. We use Forms authentication.
The other folders under Global works just fine like before.
I've tried to remove and reset the access right without any luck.