zip file problems

Hi,

I am having a problem opening a zip file.  When I try to open this file 
with WinZip it fails and throws the message: "Cannot Open File: it does 
not appear to be a valid archive".  If I try to use the Unix unzip 
command, it throws the message:                     
                                                     
kreechta:</scratch/jowells/zips> unzip classes.zip   
Archive:  classes.zip                                
End-of-central-directory signature not found.  Either this file is not a
zipfile, or it constitutes one disk of a multi-part archive.  In the
latter case the central directory and zipfile comment will be found on the   
last disk(s) of this archive.                             
                                                     
The file became corrupted when I was transfering some new data to it in
Windows and the WinZip program ended unexpectedly before the transfer was
complete.  Now the file exhibits these problems.               
                                                     
Is there anybody who can help me with this problem?  Or can you refer me to
somebody who can help?  
                                                     
Thank you very much.                                 

Best,
Josh

Joshua J. Wells, MA, Prehistory Research Fellow                               
Glenn A. Black Laboratory of Archaeology                 
Department of Anthropology
Indiana University, Bloomington - USA
http://www.gbl.indiana.edu
http://www.indiana.edu/~anthro