Field help (ITMMULT) 

Use this field to control the addition of released products to a work order.

 Sage recommend that a work order for a project should be single product only. That is, one work order for one product for one project. If this Entry transaction will be used for project-related work orders Sage advise that you leave this check box clear. With multiple products on a single work order it can be difficult to trace inconsistencies in the postings if they occur. If you click this check box to permit multiple released products on a work order, Sage advise that all additional product lines are for the same project as the first product line or blank (not assigned to a project). 

 Parameter WOPJMMSG - Block multiple projects on WO (TC chapter, PJM group)