validated Start Date

I have buy your plugin backup data base, I could do anonimous backup with it ?

Yes.

it's ok, it's send.

Thanks. (I correctly received it)

Your issue is due to configuration.
Your list of activity types starts with a specific type "Administrative", with planning mode defined as "regular".
But this type is hidden for most project types.

When displaying Screen customization for Activity, as this is not a real item, first available type is used to retreive planning mode (so using Administrative), and even if diplayed mode is "as soon as possible", constraints are used for planning "regular", forcing required validated start and end dates.
Just changing sort order of type administrative to avoid to have it first fixes the issue.

For information, issue at the origin will be fixed in V6.3
(Ticket #2853)