Async method with multiple tasks
To me it seems like you are trying to make a async task for the sake of making it async to fit in with.


  I'm trying to make my ASP.net Web API methods asynchronous


I don't see any reason for these pieces of code to be async.  They aren't doing long running tasks and aren't even hitting the db (unless Add doesn't something we don't know about of course like saves as well which is a different point of review right there).

result = await Task.Run(() =&gt;_RepositoryUser.Add&lt;DTOUser, DTOUser&gt;(user));

//use the login object to my 2nd task
var task2 = await Task.Run(() =&gt;_RepositoryLogIn.Add&lt;DTOLogin, DTOLogin&gt;(login));


Once you have removed these, the method becomes a truly synchronous method.  As it's a pretty trivial method anyway this shouldn't be a problem and making it async only confuses the issue for no benefit.