>>
>>Does someone have the ZIP file open in Windows Explorer? (it shows up in Explorer as "compressed folder" into which you are able to navigate as a normal folder)
>
>No
>
>
>>Have you checked on possibility of an antivirus blocking you? (e.g. you are updating ZIP file on network location, the moment you release access [i.e. close the file], host computer initiates an automatic scan -- blocking further updates until it finishes)
>>If the file isn't local to the computer (i.e. it resides on network share), you're more likely to run into conflicts.
>
>We are creating Zip file on local computer. Data is from local computer.
>
>
>>Make sure you've got full access to the containing folder -- sometimes you get this effect if you've don't have sufficient rights to the folder in which the ZIP file is contained.
>
>The containing folder shows 'Read only'. We we are able to do write operation from within the software as well as from explorer. The 'Read only' tag does not go.
>
>Simple command like "pkzip a.zip a.bat" does not work (even at root directory)
>
>Rakesh

Sounds like it's time to accept that PkZip is depreciated.