After updating a solution from VS2008 to VS2010 the unit tests for our custom web security providers started failing the builds with messages like:
Error 15 The type or namespace name 'MembershipProvider' could not be found (are you missing a using directive or an assembly reference?) D:\Development\[snip].UnitTests\ProviderHelper.cs
Error 16 The type or namespace name 'RoleProvider' could not be found (are you missing a using directive or an assembly reference?) D:\Development\[snip].UnitTests\ProviderHelper.cs
Error 4 The type name 'RoleProvider' could not be found. This type has been forwarded to assembly 'System.Web.ApplicationServices, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'. Consider adding a reference to that assembly. D:\Development\[snip].UnitTests\ProviderHelper.cs
The last exception here reveals the issue. The project now needs a reference to System.Web.ApplicationServices