This error usually occurs when s ript is trying to associate record to a parent record in siebel.
Scenario 1 : Active BO used in script to create association however current context does not contain child BO details.
var opty_bo = TheApplication().ActiveBusObject();
var opty_bc = opty_bo.GetBusComp("Opportunity");
var opty_con_bc = opty_bo.GetBusComp("Contact");
var opty_con_assoc_bc = opty_con_bc.GetAssocBusComp();
In this case the last instruction will error out and result into this error.
Resolution use GetMVGBusComp().GetAssocBusComp()
Scenario 2 : Parent BC has no update flag as set
Solution create thin BC which has no update flag as N, and use that bc to associate the records.
Hope it helps, please leave comments below if you face this error in some other scenario and some other trick helped you out.