Xamarin iOS - Could not load file or assembly 'System.Threading.Tasks' at startup

Question

I just upgraded to Xamarin studio 5.9 (build 431), and cannot run my project anymore. It works with a clean project though.

When I run my app, I don\'t even land in Main

Answer 1

To make a guess, I think this might have the same underlying cause as Xamarin Bug 29211.

If that's true, then there's a good chance the same workaround will work:

Under "project options -> iOS Build -> Additional mtouch arguments" add:

-linkskip=System.Threading.Tasks

If that workaround does indeed work, then it's very likely the issue will be fixed in the upcoming service release (due to be released later this week).

Update July 2, 2015

It turns out there is another subtly different common cause of the problem for System.Threading.Tasks. That second bug was originally hidden by Bug 29211 because the two bugs are very similar. The second problem is now being tracked in Xamarin Bug 31560. Note that this bug only affects simulator builds and has fairly simple workarounds, so it is minor in severity.