Hi everyone, As of a few days ago, the registration-verification certificate that has shipped with every version of Chimera for the last ten years expired. Consequently, any Chimera use after that would bring up the registration-request dialog regardless of how recently that version of Chimera had been registered. On top of that, the expired certificate caused new registrations to fail, so all you good people who were trying to help us out by registering your versions after this bug appeared were stymied. We have just released Chimera 1.5.2, which has a permanent fix for this problem. You can download it from: http://www.cgl.ucsf.edu/chimera For users who prefer not to upgrade immediately, we expect to have a solution for existing older versions in a week or less. We will send another email with details when that solution becomes available. --Eric Eric Pettersen UCSF Computer Graphics Lab http://www.cgl.ucsf.edu