I'm currently following a Microsoft guide to migrate from SBS 2011 to Server 2012 Essentials -
http://technet.microsoft.com/en-us/library/dn408633.aspx
I've previously ran through all the steps on a virtual copy of the real server to the new test server, and no real issues encountered, so I'm a little surprised to be stuck at this step.
I'm following the step 3: join computers to the new Windows Server 2012 essentials server.
However, at the point where the connect wizard (
http://server2/connect runs I get the following error;

So I'd appreciate any pointers as to where to go from here.
Thanks
It seems that when the connector is run, one should supply the administrator credentials rather than a user credentials, however, this seems badly worded when compared with the Small Business Server connectors - where it is a little more explicit that you need to supply the administrator credentials. I've done lots of connectors in the past, and have always used administrator credentials, but the wording and the guide aren't explicit enough here to avoid the obvious mistake of trying to use a 'user' for this.
Anyway, after putting in the administrator login details, you get much further and can actually join the machines to the 'new' server 2012 domain.
I have about 50% which went through no problem at all, and the other 50% all experienced the connector has stopped working and crashes. However, even though the connector crashes the machines still show up in the devices tab all set-up o.k., so as this was the whole point of the exercise then in a way this issue is resolved.
Bit scrappy really, however the issue is resolved and thanks to all the respondents.