I got same message sometimes. I can't say why it happens. With Kindle Comic Converter, try this:
Convert your files to CBZ. Doesn't matter whether input file is a CBR or CBZ file. Just select CBZ as output format. Select Kobo Glo HD as target device. I noticed it results in images with a little...
Try copying the file cheats.zip found in data\retroarch\cheats in your PS Vita to your pc, extract it there and then copy all the extracted content back to data\retroarch\cheats. That's what I'm doing right now. It's not a big file (about 80Mb), but it has all the cheat library, so it has many...