I tried to use WebSockets in my Umbraco v6.1.6 application, I changed target framework to 4.5 for this but getting YSOD when I try to save a document type:

Providing a non-null 'timeoutHandler' or a true 'executeInParallel' parameter value to the PageAsyncTask constructor is unsupported in the current application configuration. To work around this, add the following configuration switch in Web.config:
<appSettings>
 <add key="aspnet:UseTaskFriendlySynchronizationContext" value="false" />
</appSettings>
For more information, see http://go.microsoft.com/fwlink/?LinkId=252465.

If I add above line to my web.config Umbraco framework works, but websockets stop working:

System.InvalidOperationException: WebSockets is unsupported in the current application configuration. To work around this, remove the following configuration switch in Web.config:
<appSettings>
  <add key="aspnet:UseTaskFriendlySynchronizationContext" />
</appSettings>
For more information, see http://go.microsoft.com/fwlink/?LinkId=252465.

Has anyone managed to use WebSockets with Umbraco? Any advice or workaround?

Thank you.