Hi:
Please follow guideline of SAP Help and you would not get this error 
which states "
If you do not specify derivation steps for the account assignment elements of the receiving expenditures budget address, all the values of these account assignment elements will be identical to the values of the RIB object. Since the RIB object, is a revenues budget address, this will cause an error message. Therefore, you must in any case specify the value of the account assignment element commitment item."
You need to define another derivation rule specifying therein the source and target fields in the attached image , having been done with you will no longer get this error ..
Cheers 