Hello Mitch,
first of all, many thanks for your prompt response.
I just performed the steps you suggested but still, the Playmemories Online button is missing and neither I was prompted to choose whether I would like my pictures to be uploaded :-(
The strange thing is that i was given this option in a previous installation, using Windows 8.1, whereas now i use Windows 10. Thus, i do not consider that it may be a region issue...
Many thanks in advance for your support and looking forward to receiving your reply.
Cheers,
Markos