You may enter a start date for a task, and Project changes the date back to what it was before.In Figure 1, the Task Information dialog shows that Tasks 9 and 10 are linked.While on the subject of date constraints, we should say a word about the different kinds that exist.So far, we have mentioned Start As Soon As Possible (ASAP), Start No Earlier Than (SNET) and Start No Later Than (SNLT).
Keying a date for Task 3 again changed the default constraint from As Soon As Possible (ASAP) to SNET for the date you keyed.
These constraints prevent the calculation from scheduling tasks later than the constraint date.
The hard constraint types are Start No Later Than (SNLT), Finish No Later Than (FNLT), Must Start On (MSO) and Must Finish On (MFO).
It’s also hard to see when the task is more than one outline level lower than the linked summary task.
You may have to view every summary task in the task outline to find the linked summary task that’s restricting you from modifying the Task Start Date.