When deleting a task, you get following error message:
An unknown error occurred. Try your action again, if the problem persists contact your administrator
Cannot insert duplicate key row in object 'webcenter.PROJECT_WCTasks' with unique index 'projwctaskindex'
The error "......Cannot insert duplicate key row in object 'webcenter.PROJECT_WCTasks' with unique index 'projwctaskindex'" appears when deleting a task.
The same error can also occur when deleting a project (since this also deletes the tasks).
This problem is fixed in WebCenter 12.1. Please upgrade.
If it still appears in WebCenter 12.1, it probably has another cause. Please make sure the error message is the exact same. The first part is a generic part for SQL errors. Only the last part is really descriptive ("cannot insert...").
The problem occurs because we rename a task before marking it for deletion. This is to allow creating a new task with the same name as before. This renaming could fail which shows the above error. There are two possible workarounds:
First rename the task yourself to something was never used before. Only then delete the task.
Run the cleanup tool. This will remove the tasks renamed previously and therefore make name clashes far less likely.