'Step Into' is suddenly not working in Visual Studio

Solution 1:

With Visual Studio closed:

• Delete the solution's suo file (contains debug information, user settings such as break points, bookmarks, and other user settings.)
• Delete the Visual Studio cache files (see below)
• Delete all temporary files (a shift from VS9 to VS10 is that VS10 uses the temp folder)
• Manually delete all obj and bin folders using Windows Explorer.

Open Visual Studio and rebuild all. This always works. See C# VS2010 Entering break mode failed.

For reference:

Private Sub ClearVS9
    ClearFolder(oShell.ExpandEnvironmentStrings("%APPDATA%") & "\Microsoft\VisualStudio\9.0\ProjectAssemblies")
    ClearFolder(oShell.ExpandEnvironmentStrings("%APPDATA%") & "\Microsoft\VisualStudio\9.0\Recent")
    ClearFolder(oShell.ExpandEnvironmentStrings("%USERPROFILE%") & "\Local Settings\Application Data\ApplicationHistory")
    ClearFolder(oShell.ExpandEnvironmentStrings("%USERPROFILE%") & "\Local Settings\Application Data\Microsoft\VisualStudio\9.0\ProjectAssemblies")
    ClearFolder(oShell.ExpandEnvironmentStrings("%WINDIR%") & "\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files")
End Sub

Private Sub ClearVS10
    ClearFolder(oShell.ExpandEnvironmentStrings("%APPDATA%") & "\Local\Microsoft\WebsiteCache")
    ClearFolder(oShell.ExpandEnvironmentStrings("%APPDATA%") & "\Local\Microsoft\VisualStudio\10.0\ProjectAssemblies")
End Sub

See the link The evil suo file - fighting and winning with Visual Studio mentioned by JMarsch.

Solution 2:

In my case, I was stepping into a method which yielded return of an IEnumerable. In this situation, F11 may skip over the method until the IEnumerable is iterated, since its execution is deferred until then.