I have enabled the state and country picklist feature within my org. I have to refere these fields in an VF page, will the naming convention be the same as 'BillingState' & 'BillingCountry'?  What about other objects like Contacts where the field name is MailingCountry and Mailing State?

Please advise.

One of my batch class is failing throwing an exception message like
"System.DmlException: Upsert failed. First exception on row 0 with id 001G000000scGlxIAE; first error: DUPLICATE_VALUE, duplicate value found: AppUp_Group_ID__c duplicates value on record with id: 001G000000utTId:"

Let me know if there is any workaround to solve this?

I have a visualforce page which has an option o export the data from a pageblock table containing checkbox values. But the excel workbook does not show me any checked or unchecked characters when exported.

One of my batch class is failing throwing an exception message like
"System.DmlException: Upsert failed. First exception on row 0 with id 001G000000scGlxIAE; first error: DUPLICATE_VALUE, duplicate value found: AppUp_Group_ID__c duplicates value on record with id: 001G000000utTId:"

Let me know if there is any workaround to solve this?

I have a visualforce page which has an option o export the data from a pageblock table containing checkbox values. But the excel workbook does not show me any checked or unchecked characters when exported.