The best way is to start excluding parts from the analysis and running the model. (exclude, run, exclude, run) You'll want to continue this process until you've found the culprit. Once you know the beam you'll have a good idea of what's wrong and how to fix it.
All the best,
Using nicks method will both help you find the problem and also teach you a lot about how things work.
My guess is you bonded something that allowed the selections but isn't valid. Like selecting the face of beam and trying to bond it to something.
It would be nice if the software had an element comparison table that compares elements to part numbers by currently is not possible.