sorry, I understood that I was supposed to make a new topic
No a new topic for an issue you have, is only made if you don't have already an open topic about that same issue yourself.
So if you have a complete new issue (like for example bind is not working) then you create a new topic.
In this case, you are having Roundcube/webmail problems, which are related, so can all be handled in the same topic.
You could have created a new topic about the error you got by trying to log in, but since that was also already answered to here, there is no need to create a new topic for that either.
Maybe this way it's more understandable.
However, the issue you are having is strange. All should work fine. The error normally comes from some config option which DA does not use, so that is a bit odd.
And that is the reason I've suggested to send in a ticket for this issue, as chances are high that we can not solve this on the forums, it might need more investigation by DA support.