Diagnosis
The amount has not been assigned a currency.

Procedure
In the field catalog, maintain either the field CFIELDNAME or the fieldCURRENCY for the field &1 of your internal table.
The field CFIELDNAME of the field catalog should be assigned the valueof a field in your internal table which contains the currency for therow.
Example:
data: begin of itab occurs 0,
amount type de_amount,
my_curr type de_curr,
end of itab.
lt_fcat-fieldname = 'CURRENCY'.
lt_fcat-qfieldname = 'MY_CURR'.
You can enter the currency directly in the field CURRENCY of the fieldcatalog. This currency is then valid for all rows.
Example:
lt_fcat-currency = 'DEM'.