I have a photo of a painting on my hard drive which is saved as a JPEG. I have done this many times before and it has been fine, but... I am trying to edit and crop this image in Photoshop so that I can use it on a card. I normally save as a copy when I have finished so that I can keep the original. Now, I have flattened all my layers as usual and am trying to save as a copy, in JPEG. I get a warning symbol and it says' File must be saved as a copy with this selection'. The symbol is next to the selection box, 'alpha channels'. If I then save this image, all I get is something that windows is unable to open. I just don't have a clue what it means by this warning and why the 'save as copy' box gets blanked out. I need it as a JPEG to send to the printers. Thanks in advance.
What's going on is that you have added something to the picture that the JPG format doesn't support; therefore, if you save it as JPG, that "something" will be lost. It can happen with layers, texts... In your case, it's probably some selection you've made and saved.
If you want to keep that selection, you'll have to save the picture as PSD. If not, you can delete that selection, and then you'll be able to save it as JPG.