I just switched from Xcode 3 to 4. When I attempt to upload an app that I have archived to the organizer, I receive this error:
The archive is invalid
My solution was:
Open the info.plist
file in your project and in product name write your products name instead of $[PRODUCT_NAME]
The same happened to me. My mistake was I had certificates with similar names (like "Provisioning Profile of Giammy", "Profile for Provisioning of Giammy"...).
Running "Archive" from XCode 4.0 and then "Validate..." from the Organizer I faced the "app.ipa does not exist" issue. The problem was that I selected the wrong certificate from those with similar names. The "Archive" phase worked good but the archive did not pass the validation.
Solution: just picked up the correct provisioning profile in the "Archive" phase.
Lesson learned: check twice the provisioning profile name!
I was not able to solve this problem by changing or fixing code signing identities (which should resolve this problem in many cases. Nor did simply reinstalling Xcode. These are the top two solutions as I post this answer.
I found success in uninstalling all the developer tools, and reinstalling from scratch.