I have set up [Visual Studio 2012](http://en.wikipedia.org/wiki/Microsoft_Visual_Studio#Visual_Studio_2012) Professional to download debug symbols. It is set up correctly and the symbols have downloaded.

I get to the line of code I wish to step into:

```
bool result = Membership.ValidateUser("user", "password");

```

I right click on it and choose `step into specific-->Membership.ValidateUser()`

Then a tab opens in Visual Studio saying:

> 
> No Source Available - There is no source code available for the current location
> 
> 
> 

`Membership.ValidateUser()` is in the `System.Web.Security` namespace which is in the `System.Web.dll`. If I open up the Modules window I can clearly see that the symbols for this assembly have been downloaded.

If the symbols are there, why am I not able to step into the source code?