Esskay, we have uploaded the fix to your website. Please check and keep us updated, so I could mark this thread as Solved. 

Hi Ross
Thanks...but I am not understanding what is to be done now....when I click on csv data import settings I get Processing csv file whereas I have not even selected any file. It does not give me any option to do so. Please see the attached screenshot.

That means your cron is not configured properly. Try to run in manually www.site.com/ow_cron/run.php ;

ok...I did and after this I am getting the same old error -"Unknow upload error"

Clear the cache in your browser. I just run the cron on your website after uploading CSV file and I get to the second step of the import. See screenshot

ok...working...I need to do it on the production site too...can you please provide fix...?

in ow_plugins/csv_importer/forms/csv_uploader.php

there's the code: 

if ( !empty($_FILES['csv_file']) && in_array($_FILES['csv_file']['type'], array('text/csv', 'application/zip', 'application/octet-stream')) && is_uploaded_file($_FILES['csv_file']['tmp_name']) )

replace it with 

if ( !empty($_FILES['csv_file']) && in_array($_FILES['csv_file']['type'], array('text/csv', 'application/zip', 'application/octet-stream', 'text/comma-separated-values')) && is_uploaded_file($_FILES['csv_file']['tmp_name']) )

I'm going to mark this thread as Solved. 

done...great...worked for me...