Why do I see "...Invalid field npe03__Next_Payment_Date__c for npe03__Recurring_Donation__c..." when using Donations?

Our Soapbox Donations for Salesforce packages require version 2.x of the Recurring Donations package (part of Salesforce.org's Nonprofit Success Pack). If you are running an earlier version of this package (1.x), you will likely run into the following error message on your Donation form or from the Salesforce admin UI while trying to convert a lead:

 *Salesforce Error: sbxd.sbx_DonationsCampaignMember: execution of 
AfterInsert caused by: System.DmlException: ConvertLead failed. First 
exception on row 0; first error: UNKNOWN_EXCEPTION, System.DmlException: 
Update failed. First exception on row 0 with id [XXXXXXXXXXXXXX]; first 
error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, sbxd.sbx_DonationsLead: 
execution of AfterUpdate caused by: System.SObjectException: Invalid field 
npe03__Next_Payment_Date__c for npe03__Recurring_Donation__c (sbxd): [] 
(System Code) : [] (sbxd)* 

If you experience this error message, please upgrade your Recurring Donations to version 2.x. You can read about the many new features in version 2.x of the Recurring Donations package and find full upgrade instructions here.