When we define a packing for a product with UoM other than Unit category, we get an error when creating a sales order line:

Error! Conversion from Product UoM Unit(s) to Default UoM xx kg is not possible as they both belong to different Category!.

For example, we want to sell a bigbag of sand. The product 'sand' has UoM of category 'weight' and packing is 'bigbag'. This causes the above mentioned error. Second example, we want to sell 20kg kanisters (UoM also category weight), packed 21x20kg on a pallet with overpack. Packing is 'Overpack', also causes the above mentioned error.

How can we add packages to this kind of products??