Ion is the alternative to provisioning and does not require any certificates. It is irrelevant whether you have imported your certificate and provision in Graphite or Mist, as long as you are logged in with the same account, you should be fine and save. Since you have two accounts with us, are you sure you're using same account that holds the correct certificate and provision?
In order to exclude the provision as being the problem, login to Apple's dev center
-> iOS Developer Program -> Certificates, Identifiers & Profiles -> Provisioning profiles -> select the provision -> Edit and check whether the certificate you've imported in Icenium is present under Certificates.
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