Sometimes PS can be picky on the files it opens. Try opening it in a different program then saving as a jpeg.
The free Infranview will open most anything.
Awesome, this worked! Thank you!
If you saved the file in Photoshop (or some other application) under a different format but used the jpg extension, this will happen when you try to open it. The file description/info in Finder says it's jpg, but it speaks with forked tongue. For example, if you open a jpg in Photoshop, edit a layer, and save it, it will keep the jpg extension but make it a psp (Photoshop) type to preserver the layers.
To fix it, in Finder edit the extension to whatever it should be, in the above example, it's .psp. You might have to guess at what externsion it might be, e.g. tiff or png or gif.