Cannot insert the value NULL into column 'U_CTX_ALCT'

Dear Gurus,

     I have trouble when trying to add a row in the middle of a Sale Order from Head office to its brands (Intercompany transaction), the message pops up: "Cannot insert the value NULL into column 'U_CTX_ALCT', table 'FABTEK_GOLIVE.dbo.RDR1'; column does not allow nulls. INSERT fails. '' (RDR1)

     I checked the this UDF and this is for allocation with defaulted as Mandatory field. For my situation that we just do internal transaction between Headoffice and Brands, do we need to leave this UDF as mandatory, or are there any ways to fix this problem?

Thank in advance.

Regards,

Nguyen Sy Hung