The customer is trying to delete old tasks from his SMP Console. However, there is not right-click>delete option.
ITMS 7.x, 8.x
This is due to orphaned instances of the task remaining in the database.
To ensure full deletion, walk through these steps:
INSERT INTO ItemToDelete
VALUES ('<Guid>', GETDATE())
FROM [dbo].[ItemVersions] iv
JOIN [dbo].[TaskInstancesIncomplete] ti ON iv.VersionGuid = ti.TaskVersionGuid
WHERE iv.ItemGuid = '<Guid>'
AND ISNULL(ti.InstanceStatus, 0) IN (0, 1, 4)
DELETE FROM TaskInstancesIncomplete
WHERE TaskVersionGuid = '<Guid>'
If the above steps didn't work for you, please refer to KB 162337 "Unable to load or delete corrupted tasks"