It shouldn't be--which one did you download, and how? Internet Explorer, for example, sometimes has trouble with the OSX .dmg file, and truncates the name (just rename the extension or use Safari). Stuffit Expander cgave trouble a while back, but then released a new version which worked for OS 9. Too, the browser cache needs to be cleared or a corrupted download will just be reread from the cache.

Cheers.

older versions
http://www3.limewire.com/download/
http://www9.limewire.com:82/download/