Diagnosis
You want to access data on the connected rental unit for rentalagreement &V1& &V2& &V3&. However no connected rental unit has beendefined.

Procedure
Connected rental units are normally only used for particular rentalunits (such as private parking spaces with an apartment as connectedrental unit. If you want to assign a connected rental unit to rentalunit &V1& &V2& &V3&, you have to maintain this data for the respectiverental unit.