Overlap
Overlap occurs when two or more batches use one resource simultaneously. You will be warned about overlap if you run Check schedule. You can eliminate overlaps by using schedule batches or allocate.
If you do not want to be warned about overlap, do not select the Check schedule check box in the Resource group entry dialog box. Also, do not select the Check Overlap check box in the Check schedule tab of the Preferences dialog box. In the Preferences dialog box, you can specify to check overlap in just process resource groups or just tank resource groups.