I had the same problem today when I renewed my KIS subscription and then downloaded KIS 2018. Uploads to Flickr were blocked with the Flickr complaining of repeated timeouts.
Diagnosing, I found that this is caused by the Kaspersky Protection add-on/extension that the KIS 2018 installer installed automatically into Firefox. Once I disabled this add-on in my FF browser, uploads to Flickr was made possible again.
Check your browser for this add-on
Restart the browser
Next weekend when I get some free time, I will see if I can seperately uninstall this add-on. It is way too paranoid in its protection. Unless, the Kaspersky add-on development provides a white-list setting within the add-on that I can use.