Saving & Printing
Why it appears: When you save a layered document in PSD format (File>Save As and choose Photoshop from the Format pop-up menu), this warning dialog will appear if your Maximize Compatibility preference is set to ask you when saving PSD files.
How to fix it: When the dialog appears, simply click OK.
How to prevent it from happening: Go to Preferences (Command-K [PC: Control-K]) and under the File Handling section, choose a different setting in the Maximize PSD and PSB File Compatibility pop-up menu. Selecting Always will always save layers in the document; selecting Never will never save layers—in both cases without asking first.
Why it appears: A generic message that appears whenever you print to a non-PostScript printer (most inkjet printers, for example).
How to fix it: Another one of these “are-you-sure-you-want-to-do-this?” messages, so there's really no fix, unless you print to a different printer.
Why it appears: The document you're attempting to print is larger than the printable area on your chosen printer.
How to fix it: You can decide to ignore the warning, click Proceed, and print to see what happens, or click Cancel and try to fix the problem by resizing your image (Image>Image Size).
How to prevent it from happening: Try choosing Print with Preview (rather than Print) from the File menu. Then you can use the preview and click on the Scale to Fit Media checkbox if necessary.
Why it appears: You're trying to use Adobe Services to print online (File>Print Online), but your document needs to be saved.
How to fix it: Click Save and Continue to do just that, or click Cancel, save the document the way you want it, and then return to File>Print Online.
Why it appears: An error that appears if you're trying to save onto a disk that is almost full. It can sometimes appear when you've opened a file directly from a CD and have tried to save to the disc even though it's read-only.
How to fix it: Click Cancel and use File>Save As, so you can control where the file is saved.
Why it appears: Here's an “okay, thanks” warning dialog.
How to fix it: Check Don't Show Again (as quickly as possible!).
Finally, the winner of the strangest warning dialog, perhaps in the history of computers:
To be fair to Photoshop, this is a Mac OS dialog that popped up when I wanted to make sure that a series of files were associated with Photoshop. Yes, it actually asked me if I wanted to change all of my Photoshop CS2 documents to open with Photoshop CS2. Hmmm….