missing object on git-gc

I am running the git-gc tool over my repository and get the following error:
 

git-gc

...
deltifying 3308 objects...
error: corrupt loose object '<sha1>'
fatal: object <sha1> cannot be read .
error: failed to run repack
 
when sha1 is 40 bytes number 
 
Does any one know how I can solve thus issue?
 
Thanks
YOssi