Automator Action to Save as JPG

So, I'm trying to wrap up a website I developed, and I'm left with a folder of images from the previous developers which I need to generate thumbnails of to accomodate some of the new features.

Long story short, when I'm taking the original images from the website and running through a photoshop action to resize them Photoshop gives me an error saying "could not complete your request because an unknown or invalid JPEG marker type is found".

Oddly, I can open the files that are corrupt in Preview, Save As the file, and then it will open fine in Photoshop to run through the resizing action I created.

So - I'd like to automate this because 5000 photos is a lot to go through manually. I tried making an Automator action to handle the "save as" task in preview, but I suck at it.

Anyone have any tips, or direction they can give me on this?

I need an action that will take a folder of photos -> open in preview -> Save as (jpeg) -> close the photo -> open the next photo... repeat until all photos in the folder are complete.

Any help would be appreciated. Thanks!