The thread Online logs: Discontinuation of service says something about an service which allows you to download the chat logs. now its even december and I can neither read them online nor download them? what is wrong with Messenger Plus??

The service was removed completely at the end of November. That means the log download option was also removed at the end of November. That announcement was originally posted in August, there was plenty of time beforehand in which to download your logs. Its too late now.