Diagnosis
The period when a rental agreement exists for a rental unit must notoverlap that of another rental agreement. As long as the rentalagreement is valid, no other rental agreement must exist in the samerental unit which would overlap the term of tenancy.
System Response

Procedure
Select another period for the rental agreement.
If this message appears as a warning, the date up to which the tenanthas the opportunity to extend the contract, has already past. Youshould confirm this message by pressing the return key.