Hi Patrik,
I am sure you will not get this message if your Base unit is different to sales unit of measure.
I am also sure that you will get this message if you do at MM02 ( if your base unit and Sales unit are same)
Please check in MM02 under Sales: sales org1, what is the Base unit you have there and what is the Sales unit you are trying to do.
Regards, Sai krishna.