Task type can be fixed units, fixed duration, or fixed work.
Assembly: ProjectServerWebServices (in ProjectServerWebServices.dll)
TASK_TYPE controls the effect that editing work, assignment units, or duration has on the calculation of the other two fields. The options are:
0 - Fixed Units (default) - The number of Assignment Units remains constant, regardless of the amount of work or duration on the task.
1 - Fixed Duration - The duration of the task remains constant, regardless of the number of resources (Assignment Units) assigned or the amount of work
2 - Fixed Work - The amount of work remains constant, regardless of any change in duration or the number of resources (Assignment Units) assigned to the task.