conflict in the calender

I can assign task to someone in the time and another one can assign the task at the same time....why?

Dear Alaa,

Staring from v2.8 VIP Task Manager has additional servise that is a linking chain between Client and Firebird and this makes locking opened tasks difficult. At the moment several users can open the same task and make changes, the program saves all the changes, but if some of the changes are in conflict with each other, for example assigning different resourses, the last change that is saved is the change made by user who saved it the last. You can always see in the task history who made changes and what has been changed.