I found that with WinZip 12.1 if I select more than 16 files the right click context menu does not list WinZip. With 16 or fewer files the WinZip icon appears in the menu. (FYI - I had the same problem with version 12.0)
I just downloaded and installed the latest release 12.1 Build 8519 but same problem.
I am running Windows 7 Build 7100 32 bit version.
Thanks in advance for any ideas.