E2120 Required Field Missing

This type of error message indicates that Salesforce has rejected the Insert / Update because a required field on the object is not populated.This could either be a standard Salesforce field, such as Name on Account, or Last Name on Contact, or a custom field which has the 'Required' attribute set to True.

An error message example would be the following:

E2120 - ECE_SForceDataError: We got an error back from SalesForce when trying to update or insert data in SalesForce: Error returned from SFDC on create: [fields: Pricebook2Id , message: Required fields are missing: [Pricebook2Id] , statusCode: REQUIRED_FIELD_MISSING ] , Data sent: sObjects: [type: PricebookEntry , Id: Attributes: nil = "true", UnitPrice: 0.010000 , IsActive: true , CurrencyIsoCode: AUD , Pricebook2Id: , Product2Id: 01t36000001AmgCAAS .

 The above field Pricebook2Id is required and it cannot be blank. You would need to update that information in your source system before transferring data to Salesforce.