Oh, I suppose I could, you know, answer your *real* question.
In general, design warnings indicate aspects of the design that break the assumptions OR is making when it calculates drag and CP etc. So there will be some inaccuracy. Sometimes the inaccuracy if very small and you can ignore it. Knowing which warnings to ignore and which to heed is a bit of an art.
The "thick fins" warning comes from fins that are very thick compared to... um, I don't actually know the criteria. Usually you know them when you see them.
The "Open forward end" warning is from a body tube with non-zero diameter that doesn't have a closed front (usually a nose cone). The open front end of a body tube is not something that OR knows how to simulate. If it's a phantom tube that is zero-length but non-zero diameter, you can usually ensure it'll be OK by simply overriding the Cd to zero. Actually you can usually avoid this situation with judicious use of pods.
If you post the design I can give more specific explanations.