What makes a witness non Creditable enough to go to trial or even just dismiss the case? (Robbery)
That's a judgment call for the prosecutor to make. A witness's credibility is always a factual issue to be decided at trial. The court has no authority to dismiss a case on that basis if the prosecutor wants to proceed.
Besides, even if one witness has credibility problems, there may be plenty of evidence from other sources.
How many times must you post the same question?