When you launch the gantt chart for some projects, none of the project tasks are appearing in the chart (the chart is completely blank). When you try to filter for all tasks, you get a SQL error:

ORA-00001: unique constraint (schema.TEMP_WBS_GLOBAL_PK) violated

The gantt is unable to display tasks because there is more than one task with the same WBS sort value on this project. 

To confirm that this is the case, the WBS Sort column can be configured on the Task List or the following query can be run in the database: 

select  i.code Project_Code, t.prwbssequence Dup_WBS_SORT, count(*)
from prtask t, inv_investments i
where t.prprojectid = i.id
group by i.code, t.prwbssequence
having count (*)>1

To reset the tasks WBS sort on the project tasks to where the sort value will be unique, there are three options:

1. Open the affected project in OWB and without making any changes, save the project back to Clarity.
2. Open the affected project in MSP and without making any changes, save the project back to Clarity.
3. Xog the affected project out, and without making any changes, xog it back in to Clarity.   Make sure that the tasks have a TASK_ID before you xog out.  Without an ID the tasks will be duplicated per article:  Importing tasks via XOG results in duplicate tasks.

Note: Check if the project has missing IDs for tasks

Reference: WBS Sort numbers are not unique