The error message suggests to me that it can’t find the egg file at all. Maybe there’s a problem with the directory? For instance, maybe the current directory is not what you think it is, so that anim.egg is not in the current directory at the time it tries to run?
Before packing, packpanda will traverse the entire directory, sanity checking all the egg files. I think that’s what it’s doing when he gets this message. Perhaps the egg file can’t be opened for some reason or another — maybe permission bits? Or maybe it really is corrupt?
David and I have exchanged messages, and we can’t figure out what’s going on. If you like, you could zip up your project and send it to me (etc-panda3d@lists.andrew.cmu.edu) and I could try to pack it myself.