Did you resolve this?
I'm having exactly the same issue. In this case, I know for a fact that the hotlink has previously been linked into this project, successfully, and that neither the name nor the directory have changed since the last time the hotlink was successfully linked to the project. As far as I can tell, the hotlink was not deliberately deleted from the host file, but is no longer listed as a linked hotlink. It just seems to have disappeared from the host file, and there doesn't seem to be a way to get it back.
If, as you suggest, it's a problem character in the hotlink's file name, it's something that was changed with the build 5005 update, as everything was working fine before that. Is that possible? There is a "(" character in the file name, however as I said, it was working fine until recently.