Having Trouble With "Invalid" Files...

[LauraJayne]

I recently purchased a Mac. I've never had this issue before with my PC... I process my RAW files, and then pull them up in Photoshop. When I'm done I save all the files as JPGs, but when I go to pull some of them up to develop online they come up as invalid. It is every few pictures and they appear to be jpegs and even have JPG extensions. When I try and pull them up some of them come up as invalid, and then when I pull them up in photoshop and resave them, the files are fine. The other error is the pics won't load at all. These ones have somehow been saved as SUPER huge files, and I can't pull them up in Photoshop and fix them because it says the files aren't valid. I am at a complete loss as to why this is happening because I save them all the same way. Any suggestions? TIA.