From time to time I battle the “Row has been modified by another user and couldn’t be updated” when trying to update a Part. When even the usual fixes don’t work (small make change and undo, FX_Upd_Part_Trim.df, FX_Upd_PartPlant_trim.df, FX_Upd_Partwhse_trim.df, or launching the Base Part Mtc screen in Dev Mode - make change and undo).
It has been rumored you won’t see these after 10.2.200, but if someone on an old release still encounters one in the future this might work for you as well: create a small Part DMT for just that part and run it. Something like Company,PartNum,ClassID. The DMT will usually break right through the old lock that is still in place.
Paul