Updating existing records by importing data with the SDK and option: ImportModeCode.Update

I'm trying to import a CSV file to update existing records.  Right now I get "The File Type is Invalid" whenever this runs.

I'm basing this off the example code in: sdk\samplecode\cs\datamanagement\dataimport

I added a column "Account" at the beginning of the CSV: "Import Accounts.csv"

Account,src_name,src_parent,src_addresstype
5C1ED238-5837-E311-B443-000C2947CEBC,A. Datum Corporation2,Adventure Works,bill
5E1ED238-5837-E311-B443-000C2947CEBC,Adventure Works2,,ship
601ED238-5837-E311-B443-000C2947CEBC,Blue Yonder Airlines2,,bill
621ED238-5837-E311-B443-000C2947CEBC,City Power & Light2,A. Datum Corporation,bill
641ED238-5837-E311-B443-000C2947CEBC,"Fabrikam, Inc.2",Adventure Works,ship

I added this column mapping:

            #region Column Zero Mappings
            // Create a column mapping for a 'text' type field.
            ColumnMapping colMapping0 = new ColumnMapping()
            {
                // Set source properties.
                SourceAttributeName = "Account",
                SourceEntityName = "Account_1",

                // Set target properties.
                TargetAttributeName = "accountid",
                TargetEntityName = Account.EntityLogicalName,

                // Relate this column mapping with the data map.
                ImportMapId =
                    new EntityReference(ImportMap.EntityLogicalName, importMapId),

                // Force this column to be processed.
                ProcessCode =
                    new OptionSetValue((int)ColumnMappingProcessCode.Process)
            };

            // Create the mapping.
            Guid colMappingId0 = _serviceProxy.Create(colMapping0);
            #endregion

I also updated the code that creates the import to be .Update instead of .Create

 // Create Import
            Import import = new Import()
            {
                // IsImport is obsolete; use ModeCode to declare Create or Update.
                ModeCode = new OptionSetValue((int)ImportModeCode.Update),
                Name = "Importing data"
            };

Any thoughts on how to fix this?  Or how to submit data for updating existing records?

I've tried using the built-in feature of exporting the "Re-importable XML file, however that doesn't help with the particular way we need to put updated data in the system.

Thanks