Reply To: Error: File is in use

I get that error when: I use Edit Original in InDesign, but it opens in the wrong program (such as Preview on the Mac), so I go and open it in Photoshop manually (or use Edit With in InDesign). Now, when I go to save, it says it's already open. Why? Because 65% of the time I forget to close the image in Preview (or whatever app it first opened in).

Doesn't sound like that's your issue, but it's the most common similar issue for me.