Same thing on two Macs leads me to ask if you have installed any third-party software that would affect the Finder, or iPhoto/Aperture?
To troubleshoot if it is some piece of software, try booting into Safe Mode and see if you experience the problem.
Does it state where it is finding that .DS_Store file? That may be just a red herring, though.
I am not aware of any 3rd party software that I may have -- I stick with Apple products for compatability etc.
My problem is intermittent so booting in safe mode isn't going to show us much I'm afraid...the problem just randomly appears and is really quite unpredictable. The only time I see it pop up is when I go to send an email of a photo I want to share. Strange, huh?
I sent you the entire Permissions Repair info as received when I ran the utility. I have no clue what it means.
Intermittent things like that are tough to track down.
Just to see if it is a red herring, the next time you successfully attach a picture, run repair permissions and see if it shows up. If it is there when you had succes, it likely isn't the cause and we're just chasing our tail.
If that file is showing up inside the iPhoto Library, it could be the problem.
There is a glitch where you can't see the default user pictures in the dialog when you change yours. Deleting the .DS_Store file in the /Library/User Pictures folder fixes it.
Do you ever go browsing around in the iPhoto Library folder structure?