Is this a file type problem? I'm not sure I understood the question, but if you can't open them with photoshop are you saving them as something other than JPG?

I haven't tried MIR (what was that?) but make sure you run it on backups not the originals, to find out if you will loose the original?

The question is, why can't you re-size with Photoshop? Why are you using photoshop when Irfanview does batch re-size, and is free?

Something is being lost here in the translation. Photoshop, Elements, Irfanview, Paint.net (also free) should be able to open and save jpgs?