Had encountered problem “valid signing identity not found” during iOS Development. As my Dev Certificate had been expired.
By following Apple Provided FAQ Guide it is possible to solve this problem.
Following link: http://developer.apple.com/library/ios/#technotes/tn2250/_index.html#//apple_ref/doc/uid/DTS40009933-CH1-TROUBLESHOOTING_FAQ-WHAT_DOES__VALID_SIGNING_IDENTITY_NOT_FOUND__MEAN_AND_HOW_DO_I_RESOLVE_IT_
Can try to follow How do I delete/revoke my certificates and start over fresh? section and it should worked.