BusinessLayerException
 An error occurred while saving an the data to the server.
DataLayerSavingException
 Operand type clash: uniqueidentifier is incompatible with numeric
SqlException
 Operand type clash: uniqueidentifier is incompatible with numeric

Source     : MicroFour StrataFrame Business

Am I doing something wrong ?

On your business object make sure you've set the "PrimaryKeyIsAutoIncremented" property to False. By default SF sets this to True.

-Larry