The accepted answer is mostly complete, but will not fully resolve the issue.  
Here's a reproduction of my [question and answer on this issue][SO Question].

### The Problem:

In short, the problem occurs when the `MSDataSetGenerator` tool runs, but the `System.Data.DataSetExtensions` assembly has not yet been loaded into the current Visual Studio process.  

### The Solution: 

One way to load the assembly is just to open any XSD file and *THEN* re-generate the designer code.

The following steps should generate the appropriate designer file:

1. Open any XSD file to the designer view (this loads DataSetExtensions.dll)
2. Right Click on the XSD and Select `Run Custom Tool`

**Here's a full [step by step walkthrough of the issue and solution with pictures][walkthrough]**


### Other Instances:

This problem has also been reported to Microsoft in the following bug tickets:

* [#668724 - MSDataSetGenerator generates incorrect output sometimes][MS 668724]
* [#733077 - MSDataSetGenerator does not generate TypedTableBase<T> derived classes][MS 733077]


[MS 668724]: http://connect.microsoft.com/VisualStudio/feedback/details/668724/
[MS 733077]: http://connect.microsoft.com/VisualStudio/feedback/details/733077/
[SO Question]: https://stackoverflow.com/q/23661756/1366033

[walkthrough]: http://imgur.com/a/H9nwo



I'm migrating our DAL class library to .NET 4 (from .NET 3.5). We're using typed datasets quite often, and we often iterate over tables:

    foreach(var row in ds.MyTable) var tmp = row.ID;

This does not work anymore, as the designer changes the dataset's code so that tables do not derive from `TypedTableBase<T>` anymore, but from `DataTable` (and implement the non-generic `IEnumerable`). That's what the diff shows. Therefore, the row is of type `object` at compile-time.

Does anybody know if this is the usual behavior? At the moment, I'm doing it the way shown below, but I hope there's a more elegant solution:

    foreach(var row in ds.MyTable.Cast<MyDs.MyRow>()) var tmp = row.ID;
