Writing to iPhone keychaing using apple KeyChainItemWrapper

I used KeyChainItemWrapper class form apple to write to the iPhone key chain. In the first occurrence I was able to write to key c开发者_JS百科hain using an identifier. The retrieval also works perfectly. However I changed this identifier and from 2nd time onwards that iPhone key chain wont allow me to write any value to kSecValueData using a different identifier. However in the first time itself it works but not with different identifiers after that. What can be the issue here?

Thank you