I was able to resolve my problems, however i still don't know the reason.
I have to state that i also own and installed extensions from DMXZONE, maybe somehow they conflict.
Anyway i deleted the CSS Form builder (WA) and also deleted the DMX Calendar (DMXzone) then i re-installed the DMX calendar (which also made Dreamweaver crash at soem point) and suddenly this extensions worked. I then re-installed the CSS Formbuilder and guess what, the client validation option now also seems to work again.
The only issues still active:
1. when testing with localhost/..... the datepicker only shows 1 time, if from internal or external IP address then it's ok.
2. After inserting the form with css formbuilder, if re-open the formbuilder from the property inspector i can't edit the action page entry anymore, it is greyed out, why?
3. When selecting the datepicker field from the form to edit the look and feel of the datepicker i can click the OK button but nothing happens, the window stays active and i can only click CANCEL or HELP.
4. Inside the CSS Formbuilder itself when creating a datepicker field, besides this field there is an edit button which is not active. Should you be able to edit the datepicker itself from within the CSS Formbuilder or not?
5. Last but maybe that's normal is that after installing all extension (WA and DMXzone) Dreamweaver launches much slower and also opening the first page inside DW and launching some extensions takes much longer to open. Do these extensions make internet contact while launching Dreamweaver? maybe this makes everything slow?
Thanks again for all the feedback and support.
Thanks for all the feedback and support