I also had problems with Winzip.  

Luckily I also have Winrar and used that to extract the files to the subdirectories.  I then used Winzip and re-zipped it.  I could then use Winzip on the new file.  It is possible that the original Winzip used for this is bad and needs to be reloaded, or  there is a status in one of the subdirectories that the usually very reliable Winzip can not handle.

Hmmm ....