Method Error 'Cannot await 'System.Threading.Tasks.Task' from await and async properties

Question

I have installed the NuGet Package Async for .NET Framework 4, Silverlight 4 and 5, and Windows Phone 7.5 and 8.

Version 1.0.16

I am using Microsoft .NET 4.0 and I can not upgrade due to Web Hosting Package Restrictions. (Sadly!)

My test Code: (I am doing a Linq to SQL Query in place of Thread.Sleep)

public class Search
{
public async Task<List<Result>> GetResults(string SearchString)
{
await System.Threading.Tasks.Task.Factory.StartNew(() => Thread.Sleep(1000));
}
}

My Error:

Cannot await 'System.Threading.Tasks.Task'

http://blogs.msdn.com/b/bclteam/p/asynctargetingpackkb.aspx talks about the error but it is not really the answer as I am not using VB and I am already doing what the solution describes.

[EDIT] I am getting a warning:

Warning 4   The primary reference "Microsoft.Threading.Tasks, Version=1.0.12.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" could not be resolved because it has an indirect dependency on the framework assembly "System.Runtime, Version=1.5.11.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" which could not be resolved in the currently targeted framework. ".NETFramework,Version=v4.0". To resolve this problem, either remove the reference "Microsoft.Threading.Tasks, Version=1.0.12.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL" or retarget your application to a framework version which contains "System.Runtime, Version=1.5.11.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a".

Thanks for your help.

Answer 1

What a Nightmare! I have found the problem.

Microsoft.Bcl

It appears in my case that the Microsoft.Bcl and Microsoft.Bcl.Async are in conflict. I removed the Microsoft.Bcl and Microsoft.Bcl.Async with the following commands:

uninstall-package Microsoft.Bcl.Async -force

then:

uninstall-package Microsoft.Bcl -force

and then install again:

install-package Microsoft.Bcl.Async

Now it works a charm. I cant believe this? Also not sure as to why Microsoft.Bcl was left there in the first place. After removing Microsoft.Bcl.Async it gets left behind. So far all works fine. Some more testing to be done.

If others have issues with NuGet Packages, you can try at your own risk:

update-package -pre

This will try to roll back packages that have been updated. This is how I found the issue.

[EDIT] Its worth noting after further testing, Microsoft.Bcl is not removed when one uninstalls Microsoft.Bcl.Async. Microsoft.Bcl can be updated separately and it appears this update outside Microsoft.Bcl.Async may be an issue. Microsoft.Bcl is installed when one installs Microsoft.Bcl.Async.

Hope this helps others!