The F9 is Canceled when i close the project

Hi everyone, 

I have a probleme with a project in P6, the dates ( delta of 1 minute but the date change to the day after )  of about 30 activities (30/1600) changes when i close and re open the project. I think that the problem comes from the excel that we import in order to change the ressources. So when i remove the ressources its all ok but, so i try to add the ressources back... same problem

i tried to add another activities with the same sittings it remains the same. 

thanks a lot for ur help!