My blog reader has a problem. He explained it step by step, and I will answer at it in the same way.
Project in certain instances doesn’t flag over allocated resources.
For example, I created a resource John and assigned him to the project at 50% (Max Units):
Then I assigned this resource to a task at 51% that exceeds its max units of 50%. In this case Project was supposed to flag John as over allocated resource, but it did not do that. The only place where Project show over allocation is in in the time phased portion of the Resource Usage view:
Is it a BUG? No! Is it an over allocation? It depends.
In this particular case, this is not over allocation because of setup:
John is assigned to the Task with 51%. It means that he will work 51% of 8 hours = 4,08 hour per day, and he is supposed to work 4 hours per day MAX, because of his 50% availability. So yes, John is over allocated per day (as you can see in Resource Usage View), but since Levelling Options is setup to Week by Week (or maybe Month by Month) generally John is not over allocated. WHY? Because John should work max. 20 hours per week (5 days * 8 hours per day * 50% = 20 hours). Task1 has 3 days duration, and John is assigned with 51% which means that he will work 3 * 4,08 = 12,24 hours in particular week, which is less than 20 hours, so he is NOT over allocated. If I put Day by Day in field mentioned above I will get:
Now John IS over allocated because he is supposed to work no more than 4 hours per day (no matter how many hours he will spend in one week).
When I assign John at his Max. Units (50%) or less to both tasks Task 1 and Tasks 2 that have FS relationship, Project behaves as expected as no over allocation for John is detected.
But when I assign John to both tasks as above, but at any capacity higher than his Max. Units, e.g. at 51%, Project marks John as over allocated although he is not as the tasks don’t run concurrently.
Again, since overallociation is set up to Week by Week, now John IS over allocated. Why? He is supposed to work 4,08 the whole week, which means he is supposed to work 5 * 4,08 = 20,4 hours in this particular week, but his maximum capacity is 20 hours per week.
On the other hand when I add a lag to Task 1, Project behaves as expected and doesn’t show over allocation with the strange exception in the time phased portion of the Resource Usage View where the work is displayed in red as being over allocated:
Again, everything works perfect. Since overallociation is set up to Week by Week, now John IS NOT over allocated. Why? He is supposed to work 4,08 for 3 days in a week (because of Lag) , which means he is supposed to work 3 * 4,08 = 12,24 hours in this particular week, but his maximum capacity is 20 hours, and 12,24 is less than 20 hours, so John is NOT over allocated. But he is over allocated in a single day, which is shown in Resource Usage View.
To conclude, before you want to deal with over allocation, be aware that you set it up in a right way (Day by day, Month by Month and so on).