I hear you, sorry for the frustrating experience!
Gustavo forgot to mention that we've patched the 2.6.1 version almost immediately after having released it, only a few quick updaters like you have got that issue. We want to include other important fixes in our next release before we do so, so that we don't bother you with daily updates.
Anyway if you want to fix it on your site before we release the new version 2.6.2, simply:
1 - Go to your WordPress' plugins panel
2 - Deactivate MailPoet
3 - Delete it (rest assured you won't lose your data)
4 - Install again from the WordPress repository.
Try that and let me know how does it go.
On a side note: even if we keep an eye on that forum, it's actually difficult for us to follow its activity.
Try as much as you can to write us directly from our contact page which is the direct line to our support team.