The typical program verification system is a batch tool that accepts as input a program annotated with Floyd-Hoare assertions, performs syntactic and semantic analysis on it, and generates a list of verification conditions that is subsequently submitted to a theorem prover. When a verification condition cannot be proved, this may be due to an error in the program or an inconsistency in the annotations. Unfortunately, it is very difficult to relate a failing proof attempt to a particular piece of code or assertion. We propose a solution to this problem using the technique of origin tracking.