After many complaints (what Ubi refer to as "feedback" ), Ubisoft have scheduled a transfer of their server resources in order to - hopefully - improve the online resources of several of their games. Naturally, during this transition there will be downtime for several games, including Heroes VI, from February 7th. at 20:00 EST:

This list shows which games will and will not be affected. As you can see, H6 is on the list of games that will not be playable during the transition.

Regarding Uplay:
"Uplay PC will be not be available during the transition.
PC games will remain available for all players who have already connected at least once."

We agree whole-heartedly with the sentiment that the online features have been ... I'll be kind: lacking and we applaud the move of boosting the online resources.

One of the fans' dislikes with H6 thus far has been the game's dependence upon it's online features. That if the servers go down, the whole game becomes unplayable due to the integration of savegames with the Conflux. This upgrade is therefore welcome, though we maintain the view that offline features should be completely unaffected - completely severed from Ubisoft's servers.