[TechniSol]

While I agree that ALL software should be able to process errors without abends (abnormal ends) and that more information than a screen that merely displays "processing" should be considered A REQUIREMENT, not an option, one does have to be realistic...

Reality #1: Ereaders are designed and sold as a conduit to further content from which the manufacturer expects to profit. We all know this, why are we so surprised? They aren't really sold to work with any file that just happens to have the right extension. I'm not saying that should let them off the hook, but it's not like the OP bought a Kobo book and couldn't get the reader to process it. Perhaps the OP's conversion process may play a role in the difficulty he is having? Nowhere did the OP detail the conversion or verification process, though there was a mention of calibre. Did he even run them through SIGIL or a similar product that can perform verification?

Reality #2: With number 1 in mind, perhaps the OP would get further requesting help from Kobo and making a suggestion regarding a more enlightening system than merely displaying "processing".

Reality #3: Rather than attempting to process in excess of two hundred files multiple times one might have divided them into manageable groups and attempted to process them so that the objectionable files could more easily be found by sub dividing until the errant files were discovered.

While I understand the OP's frustration, there were mitigating strategies as pointed out above...