I have a 87.24 GB tar file (87241052160 bytes) that Zipeg won't open. After Zipeg starts and I try to open it, or if I "Open With" from the finder, Zipeg reports the same result. A window appears saying:
failed to open archive
"my-filename.tar"
the file is corrupted or file format is unsupported
This tar file is however just fine. It was made with the command-line tar on Mac OS X, and the command-line tar handles it just fine. I'm guessing it's the size, but I haven't tested that.
I can't give you this file, but if you take a disk with a bunch of files totaling about 87 GB (of maybe even 5GB) you may be able to reproduce the issue easily.