OCR is inconsistent?

[MadhumithaTP]

Im trying to perform OCR on a LCD meter. The image of the same has been included below. The middle four lines seem to get detected alright. Ive used a different character set file for the topmost line (which reads "Summary"). The program (has been attached below) runs fine and "summary" gets deteced on some executions. When run again in a couple of seconds(set up is undisturbed) , a '?' appears instead of summary. Is there any excution flow problem in my code or is Vision OCR Training inconsistent?