Hi
as you see in page error message this is obviously related to your Scenario customization, it seem you have wrong setting for "Cost Center". based on your clarification i believe due to some form configuration after some events in your form the value of cost center have disappeared and caused this error message. i recommend you to check your event and find which event cause this problem. some time some standard events like Initialization and Check may do this to some field which you need to be aware of.
In this case you need to check that you add those field to your Scenario Stage and also whether you use standard backend (PA,PT,PD) or BAdI Service you have to add your field to your backend fields. for this purpose you can manage all in HRASR_DT and check against these settings.
Hope this Help.