Scenario
When the Advanced Bill of Materials (BOM) feature is enabled and the Mass Create Work Orders page errors out, "You must enter at least one line item for this transaction", this means the Work Orders created by the system do not contain any line items.
This behavior can be caused by the Bill of Materials linked (shown under Manufacturing tab > Bill of Materials sub tab) to an Assembly Item is set to be Default for a different Location (e.g. Location A) when the Mass Create Work Orders page is set to create Work Orders for a different Location (e.g. Location B).
It is also possible that the BOM is neither set as a Default for any Location nor as a Master Default.
Solution
To resolve, either set the BOM as Default for the Location, where the Work Orders are created for, or set the BOM as Master Default to make it available for all Locations.