I've been using RoundCube Webmail ( http://wiki.dreamhost.com/RoundCube ) for about a month now for a few domains. I like it, however I have received several complaints that it dies with 'invalid session' frequently while composing messages. It seems to happen when it tries to save a draft of the message, but fails and logs out.
This sucks, because you loose the message you're working on. If you're lucky, some of it might be in your drafts folder, but it will be an earlier draft.
Has anybody else experienced this problem? Can anybody offer a solution?