Trouble running app on device?

I was able to run my apps on my ipod a few months ago but now for some reason they give me this error..

Code Sign error: The identity 'iPhone Developer' doesn't match any valid certificate/private key pair in the default keychain

i have looked on here for the same problem and found several, but none that seem to help me. i ran the development provisioning assistant online but i noticed on part of it after i downloaded and installed the provisioning profile and got to this step..

Step 3: Verify your private and public keys in Keychain Access

i noticed that when i click on "keys" there is nothing there.

When i click on "all items" i see the certificates t开发者_开发问答here but there are no keys.

I am lost, does anyone know how to fix this?

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Is it possible your certificate had expired? You can try downloading the certificate again and add it to keychain. In certificate's details on apple provisioning site, check if your provisioning profile is listed or not.