Type-based program verification, which reduces program verification to type inference, has been used as a lightweight approach to automated program verification. Whilst it is often effective and faster than other methods such as model checking, the type-based approach often fails to provide useful information upon a failure of the verification. We address this problem for a recent type-based verification tool called ConSORT for imperative programs. Producing a useful error message is particularly challenging for ConSORT, as the underlying type system combines the notions of ownership, refinement types, and context-sensitivity. This paper pro- poses a method to produce error messages for ConSORT and reports an implementation and experimental results. The proposed method is potentially useful also for other type-based tools for automated program verification.