there're indeed some changes in RhoMobile, especially in the build script and the rakefile that got a major update around v4.0/v4.1 to support multiple Android architecture (ARM and Intel x86).
Your best option would be to generate a new project and copy your existing models, controllers and views (plus the static files) into it.
Depending on the features used in the original app, it can be really just a copy and past process or it may involve some updates for some files (like the Settings controller).
Trying to open your older project (coming from Rhodes or RhoMobile v2.x) is probably not going to work due to the changes in the rakefile.
Thank you so much for your answer.