Leon - low-values is not a numeric value, it is of course hex zeroes, i.e. x'00000000'. which cannot be moved into a numeric field. It can be moved into a character field, pic x(4) for example.
Why are you trying to move low-values into a numeric field? you can always move it to a PIC X field first then test the field to see if it numeric, or low-values, then move to the numeric field if it contains a numeric value?
Suggest you move a valid numeric value to a numeric field. . . Zeros should work nicely
If you force non-numeric values to a numeric field you will probably cause someone (you or another who has to deal with this code next year when it is no longer fresh in your/their mind) an unwelcome surprise.