Andrea,
I checked the User security again to ensure that they match. I am logging in with their usernames from the same workstation in our Dev environment.
Below is the Debug trace from Dexterity. This is for the user that the posting completes.
For the user that does not complete, that traced reaches the very top line of the trace below and goes no further. ('IsRequired() of form POP_POLINE')
10:21:51 B: 'IsRequired() of form POP_POLine', 0, 1-
10:21:51 'View_Add_POPLine', table 'POP_POLine', 8
10:21:51 'POC_Activated() of form POE_PO', 0, 0
10:21:51 'Timer_Refresh() of form POE_Cache', 0, 1
10:21:51 'Timer_Reset() of form POE_Cache', 12:00:00 AM, 1
10:21:51 'SQLPath', 2277, 3, 0, ""
10:21:51 'OSRC_POP_POLine_Update', table 'POP_POLine'
10:21:51 'ICJC_LE_Update_PO', table 'POP_POLine'
10:21:51 'SQLPath', 346, 10, 22020, ""
10:21:51 B: 'GetCurrOrdQty() of form POP_POLine', 0.00000, 1-, table 'POP_POLine'
10:21:51 B: 'IsParentLine() of form POP_POLine', 0, 1-
10:21:51 B: 'IsBlanketPO() of form POP_POLine', 0, 1-
10:21:51 B: 'Get() of form POP_PORcptApply', 0, 1-, table 'POP_PORcptApply', 23, "", 0
10:21:51 B: 'Get() of form TableObj', 0, 1-, table 'POP_PORcptApply', 23
10:21:51 B: 'Destroy of form POP_POLine', 1-, table 'POP_POLine'
10:21:51 B: 'Destroy of form POP_PORcptApply', 1-, table 'POP_PORcptApply'
10:21:51 B: 'GetPostingBackOrderedItems of form popBackOrderedItemsRpt', 1-, 3-, table 'POP_ReceiptLine', 10/30/2020
10:21:51 B: 'GetItemID() of form POP_ReceiptLine', "", 3-, table 'POP_ReceiptLine'
10:21:51 B: 'GetSiteID() of form POP_ReceiptLine', "", 3-, table 'POP_ReceiptLine'
10:21:51 B: 'ExistsForReceiptItem() of form popBackOrderedItemsRpt', 0, 1-, "CAQUAL8560.098", "MAIN"
10:21:51 B: 'SetIndexItemID of form popBackOrderedItemsRpt', 1-, "CAQUAL8560.098", 1, 0, 0/0/0000, "", 0
10:21:51 B: 'Get() of form popBackOrderedItemsRpt', 0, 1-, 13
10:21:51 B: 'Get() of form TableObj', 0, 1-, table 'popBackOrderedItemsTemp', 13
10:21:51 B: 'GetItemID() of form POP_ReceiptLine', "", 3-, table 'POP_ReceiptLine'
10:21:51 B: 'GetSiteID() of form POP_ReceiptLine', "", 3-, table 'POP_ReceiptLine'
10:21:51 B: 'GetUnlinkedSalesItems of form popBackOrderedItemsRpt', 1-, "CAQUAL8560.098", "MAIN"
10:21:51 'SQLPath', 0, 2, 156, ""
10:21:51 B: 'Create() of form SOP_SOLine', 0, 0-, table 'SOP_LINE_WORK', "", 0, 0, 0
10:21:51 B: 'SetRangeTrxSourceByItem of form SOP_SOLine', 1-, table 'SOP_LINE_WORK', -, -
10:21:51 B: 'Get() of form SOP_SOLine', 0, 4-, 11
10:21:51 B: 'Get() of form TableObj', 0, 4-, table 'SOP_LINE_WORK', 11
10:21:51 B: 'IsCommitments() of form popBackOrderedItemsRpt', 0, 1-
10:21:51 B: 'MoveToHist() of form POP_ReceiptLine', 0, 3-, table 'POP_ReceiptLine'
10:21:51 'SQLPath', 0, 3, 159, ""
10:21:51 'FA_TRIGGER_ADD_POP_ReceiptLineHistNew', table 'POP_ReceiptLineHist'
10:21:51 'SQLPath', 309, 1, 22000, ""