why is my iPhone ‘Unable to Sign or Encrypt’ ?

On my Mac-Pro I have used the iPhone Configuration Utility Version 3.4 (283) to add my email SSL certs (Credentials) and root certs from COMODO (an Apple approved CA) but for email accounts other than my primary, I get this error message: “Unable to Sign or Encrypt”” “because identities for the address” something@somewhere.com “could not be found”

I have an iPhone 4

Is anyone able to offer any advise on this?

Many thanks