I read something somewhere about this exact problem. I believe you just need to send BTC from that address so it is known. I could be wrong, and I cant remember where I read it.
Good luck
Sorry for interrupting the discussion with an unrelated question regarding the masterchain.info-wallet (I didn't know where else to post; couldn't register at mastercointalk because never received the confirmation e-mail):
I've tried to use the masterchain.info-wallet for the first time to sell 1.0 MSC on the distributed exchange. However I do not succeed with this task, because I'm unable to verify my sender address which is needed to create a sell offer. When I click "verify" after entering my seller address (which is exactly the one on which I've received the MSC earlier) I always get the following error "no pubkey on blockchain. use wallet or supply Public Key from brainwallet.org".
The same problem occurs when trying to send MSC.
What am I supposed to do to get this working? What kind of public key is needed?
Thank you for any help you can offer.
ya.ya.yo!