If you debug then you might find the field, from the error it is not possible as it is a general error used for any of the unit fields.
If you look closely at the message then you can see a small gap between the word "measure" and "for material" . Here is a variable that should tell you the unit.
Since it is empty it can be assumed that you missed to enter a unit.
So you can go into step 5 and just do a search on "unit" to find all fields.
I think I see already where where the unit is missing when looking at the converted data screen shot.
The second field in BMMH6 structure is a unit field, and do not see any unit there.
As it is the first record it should be the same unit as the base unit.
Look into the alternative unit data of an existing material and see how the first line appears, look then as well into table MARM to see how it is technically. This way you need it in BMMH6