From Archive::Zip

If the name given does not represent a readable plain file or symbolic
+ link, undef will be returned
[download]

It looks as though $renamed_file is not "a readable plain file or symbolic link".

Try wrapping your code with this check to be sure:

 
if ( ( -r $renamed_file )&& ( ( -f $renamed_file ) || ( -l $renamed_fi
+le ) ) ){
   #add to zip
}
else{
   print "$renamed_file is not a readable valid file id\n"
}
[download]