Hi,
Those records are not duplicates.for the same customer number there are diff customer sales area and different partnerfunctions etc. so there are many number of records for same customer number.
Multiple data records with the same key is known as duplicate data records.
As the key in MD table is only Customer number, those records will be considered as duplicates and if you select that handle duplicate records check box in DTP u will not get the error but the records will get overwritten as the last data record in the data package is interpreted as being valid and is updated to the target....
In your case compounding should work perfectly....can you be more clear on that 60 char length part issue ?