XSD 파일을 포함한 프로젝트 - The type or namespace name 'TypedTableBase<>' does not exist in the namespace 'System.Data'

제 경우에, 기존 .NET 4.0 프로젝트를 .NET 4.6으로 Target Framework을 변경했더니, 곧바로 다음과 같은 예외가 발생했습니다.

Rebuild started...
1>------ Rebuild All started: Project: Jennifer40.WebSiteTest4, Configuration: Debug x64 ------
1>C:\temp\MyTestWebApp\AccountDataSet.Designer.cs(280,69,280,95): error CS0234: The type or namespace name 'TypedTableBase<>' does not exist in the namespace 'System.Data' (are you missing an assembly reference?)
1>C:\temp\MyTestWebApp\AccountDataSet.Designer.cs(395,59,395,64): error CS0115: 'AccountDataSet.AccountDataTable.Clone()': no suitable method found to override
1>C:\temp\MyTestWebApp\AccountDataSet.Designer.cs(403,62,403,76): error CS0115: 'AccountDataSet.AccountDataTable.CreateInstance()': no suitable method found to override
1>C:\temp\MyTestWebApp\AccountDataSet.Designer.cs(442,60,442,77): error CS0115: 'AccountDataSet.AccountDataTable.NewRowFromBuilder(DataRowBuilder)': no suitable method found to override
1>C:\temp\MyTestWebApp\AccountDataSet.Designer.cs(448,52,448,62): error CS0115: 'AccountDataSet.AccountDataTable.GetRowType()': no suitable method found to override
1>C:\temp\MyTestWebApp\AccountDataSet.Designer.cs(454,37,454,49): error CS0115: 'AccountDataSet.AccountDataTable.OnRowChanged(DataRowChangeEventArgs)': no suitable method found to override
1>C:\temp\MyTestWebApp\AccountDataSet.Designer.cs(463,37,463,50): error CS0115: 'AccountDataSet.AccountDataTable.OnRowChanging(DataRowChangeEventArgs)': no suitable method found to override
1>C:\temp\MyTestWebApp\AccountDataSet.Designer.cs(472,37,472,49): error CS0115: 'AccountDataSet.AccountDataTable.OnRowDeleted(DataRowChangeEventArgs)': no suitable method found to override
1>C:\temp\MyTestWebApp\AccountDataSet.Designer.cs(481,37,481,50): error CS0115: 'AccountDataSet.AccountDataTable.OnRowDeleting(DataRowChangeEventArgs)': no suitable method found to override
========== Rebuild All: 0 succeeded, 1 failed, 0 skipped ==========