Maybe, Dirk, if you edit your user details and remove the hyphen, you'll be able to connect. I see in the Mumble log file that you've connected as EHM2581_Dirk in the past... so you were issued a certificate at that time (although it probably does not exist on your compute anymore, since the major upgrade).
From that same log file, I indeed see you tried 7 times this morning; to no avail:
<W>2013-12-04 07:44:44.960 1 => <61:(-1)> New connection: ***.***.**.**:*****
<W>2013-12-04 07:44:46.314 1 => <61:(-1)> Client version 1.2.5 (Win: 1.2.4-194-g829d4c6)
<W>2013-12-04 07:44:46.501 1 => <61:EHM-2581_Dirk(-1)> Rejected connection: Wrong password for user
<W>2013-12-04 07:44:46.643 1 => <61:EHM-2581_Dirk(-1)> Connection closed: [-1]
It says "wrong password for user", so that's why I assumed you had used a password. But that might just be a generic error message to reject the connection for other reasons as well (or maybe this version does not accept an empty password field, or it fills it with a space character, or... etcetera)
What surprises me is the client version: 1.2.5, where 1.2.4 is the latest. So digging around for that, I noticed at the Sourceforge site that you have the option to choose from two downloads for Windows: "1.2.4 (stable)", and "1.2.4-194-g829d4c6 (Snapshot)". From the last part of the line in the log file, I assume you took the latter one, where I know for sure I downloaded the first (stable) one. If you are to re-install the Mumble client, be sure to download the stable version, as that one is the official release one (the other one is a pre-release for 1.2.5, I think).
Here's a link, since I had it open in another tab already:
http://mumble.sourceforge.net/