Not seeing help content of Windows apps in Parallels
Installation of version 6.0.11992, the newest release of parallels desktop, fixed the problem. Installing a new release also reinstalled the parallels desktop tool and relinked the shared folders.

It took about 5 days for the release to be visible for the parallels updater after it was available. But once it was, all worked like a charm.

My problem took place over Christmas, and I was helped wonderfully through these days. I want to thank the people of Parallels support team. (I have to blame myself for spending my time with this problem instead of taking time to worship the king.)

What the problem was never really became clear. But thanks for your help.