To Reproduce:

1. Open the attached project, an 'Internal compiler error' is thrown because of the 'yield break' in line 70.

2. If you use a different yield statement for example 'yield return null' instead you get the expected 'The yield statement cannot be used inside anonymous method blocks' error.

3. The compiler doesn't break if the MyCallback delegate is defined outside and only passed to the new coroutine, then you also get the expected error.