.NET 4.0 application with Microsoft.Bcl.Async fails to build on .NET 4.5 build server

.NET 4.0 application with Microsoft.Bcl.Async fails to build on .NET 4.5
build server

I have a .NET 4.0 application which uses Microsoft.Bcl.Async for
async/await support, developed under Visual Studio 2012 in a Windows 8
machine. It builds fine in my machine and it runs fine in other
environments (XP/Vista/7).
My build server setup is Windows Server 2008 R2, .NET 4.5 installed and
TeamCity.
My build configuration fails to build my solution, with the following error:
GenerateTemporaryTargetAssembly
GenerateTemporaryTargetAssembly
Ferox.Local.Wpf\uf4edrwb.tmp_proj
CoreCompile
Csc
MyClass.cs(8, 29): error CS0433: The type 'System.IProgress<T>' exists in
both 'c:\Windows\Microsoft.NET\Framework\v4.0.30319\mscorlib.dll' and
'c:\TeamCity\buildAgent\work\80d9f16a33820be7\packages\Microsoft.Bcl.1.0.19\lib\net40\System.Runtime.dll'
The build configuration is set to Visual Studio 2012. I've checked the
agent requirements and it includes a dependency on
"DotNetFramework4.5_x86". Hence it must be using .net 4.5 msbuild, as
stated here.
I've removed the packages (Microsoft.Bcl.Async, Microsoft.Bcl,
Microsoft.Bcl.Build) and added them again. No difference.
I'm running out of options. Any ideas?
EDIT
As I said, I've just set TeamCity and my build configuration is pretty
simple. First it checks out the branche from svn.
It has a build step with runner type "Visual Studio (sln)", Visual Studio
version is 2012, "Targets" field is "Clean, Build", and the configuration
is "Release".
Additionally it uses "AssemblyInfo patcher" to update the version number.
UPDATE
I've followed Jon Skeet's suggestion and changed the runner type do
MSBuild. Runner type: MSBuild MSBuild version: Microsoft .NET Framework
4.5 MSBuild ToolsVersion: none Run plataform: x86 Targets: Clean, Build
Command line parameters: /P:Configuration=Release
It still gives me the same error.
I've changed the "MSBuild ToolsVersion" to "4.0" (even though I don't
think there is any need, because the solution was created with Visual
Studio 2012). Same error.
I've changed "Run plataform" to "x64". Same error.