I've just acquired a new Macbook (to replace an older Mac mini) and am setting it up as my new development machine. When I do a build of an app that I've already released on the app store, Corona tells me that it built but it failed to pass Apple's validation tests.

A summary of what I've done so far:
- exported private key from old machine and imported to new machine
- exported developer and distribution certificates to new machine
- exported provisioning profiles to new machine

On the new machine, I see:
- in Keychain, the private key (but not the public key)
- in Keychain, dev and dist certificates
- in Xcode, distribution & developer identities
- in Xcode, adhoc & appstore profiles, with no errors shown (e.g. of no matching keys)

I've tried to export/import my public key to the new machine but Keychain fails to import it. Is this the cause of my problem? It seems to be the only difference I can see between the two machines, looking at Keychain and Xcode.

Is there anything else I need to do to migrate to a new dev machine? I don't know if it makes any difference but the new machine is running Lion and the old one is running Snow Leopard (and is too old to run Lion).

I got a new iMac and had to transfer provisioning profiles, private keys and certificates.
Follow the instructions carefully below.
This will transfer everything you need, provisioning profiles, private keys and certificates.

To export your digital-identification items to a secure file, follow these steps:

Open the Xcode Organizer on your old computer.
In the DEVELOPMENT group, select Developer Profile.(top left, usually the first in the list)
Click Export Developer Profile.
Name the file, select a location for it, enter a password to secure the file, and click Save.
Now, when you need to develop iOS applications on another computer, import your digital-identification items into it by performing these steps:

To import your digital-identification items to the new computer, follow these steps:

Copy the developer-profile archive to the new computer.
On the new computer, launch Xcode.
Open the Organizer.
In the DEVELOPMENT group, select Developer Profile.
Click Import Developer Profile.
Locate the archive, enter the password used to secure it, and click Open.

Thanks for your detailed response! It's a simpler process than the one I was following. All sorted now.