Activity Tracking
To prevent the possibility of two imports running simultaneously that are attempting to create/update the same records, both BOM Import and Routing Import add activity records to the Batch Activity table (DYNAMICS..SY00800).
When an import starts it adds the activity record and removes it upon completion. During this time if another user attempts to run an import they will receive an error message at the bottom of the window, as shown below.
In the event an activity record gets stranded, open the window again and it will clear the record.
If needed, delete SY00800 where BCHSOURC is MFGIMP.