Big planned date issue

Hi !
I have a big problem with planification and planned date : I have 41 elements (activity and milestones) with planned end date before planned start date. I tried to modify it on database, and run automatic plannification, but the issue occurs again.

With this problem, I can't change anything on the element form.

Have you ever seen this before ?
Thank you by advance.
Cédric

Hello ,
I have try the same case , i have the error when i don't calculate the planning manualy .
Try to calculate planning with the button calculate planning ( see attachment ) .

With automatic calculation or manual calculation, it is the same...

Oh ... I will work on this anomaly and i will return to you

Have you got assigned work for your resource in assignment ?

No, not for this activity. Ressources for this element are external.