Hi Mark,

I was able to reproduce the issue, in the meantime, you can use the following workaround to set your project with concurrency level: Thread.

1. Open EiffelStudio and Create a new project (suppose you use concurrency)
    a) Delete the precompiled library from the project settings [ProjectSettings-> Target -> Groups -> Precompile: base_pre]
    b) Exit from EiffelStudio
2. Open the project with Clean Compile
    a) Open the Project Settings and set Capabilities [concurrency: Thread]. 
    b) Exit from EiffelStudio.
3. Open the project with Clean Compile
    a) Open Project settings and confirm that concurrency is: Thread.


  -- Javier