Update: There is a hotfix now available to address this issue, though you have to ring MS support directly to get hold of it at the moment. The plan is to roll it into an IE9 update in the near future. More details can be found here
There is a known issue with the Exchange 2007 and Exchange 2010 Management Consoles on machines with Internet Explorer 9 installed. This issue causes you to recieve the error: “You must close all dialog boxes before you can close Exchange Management Console.” when trying to close the EMC even though there aren’t any dialog boxes open.
As it stands, there are several workarounds: You can uninstall IE9, you can kill the MMC process from task manager every time and a few people have reported success with turning off “Internet Explorer Enhanced Security Configuration” for Administrators and Users (Servers only) and then adding https://localhost to the “trusted sites” in IE.
According to the Senior Program Manager for Internet Explorer Product Quality, Mark Feetham:
[...]we do now understand what’s occuring between the EMC, MMC and MSHTML. We have enough information to complete the investigation and have moved to looking at ways to improve this situation.
Rumoured ETA for a fix is Q4 2011.
It would appear that the Exchange 2010 EMC isn’t particularly bright; when you launch it, it picks a CAS to connect to from AD. This is fine.
However, should that server cease to exist, by which I mean Exchange is uninstalled and it is properly decommissioned, then the EMC will continue to try and connect to it. Even after the connection fails, it’ll keep on merrily plugging away at the non-existent server, never considering that there are probably other servers it could try.
This is very annoying and seemingly very stupid behaviour. To work around it, close the EMC, fire up your registry editor of choice, locate the following key:
HKCU\Software\Microsoft\Exchangeserver\v14\AdminTools\ and delete the
NodeStructureSettings value. This will reset the EMC and cause it to pick a new CAS to connect to; it may also affect other settings that you’ve changed in the console.
Another option is to close the EMC, navigate to
C:\users\<username>\AppData\Roaming\Microsoft\MMC\ and delete the
Exchange Management Console file. This will also reset the EMC and will definitely reset any customisations you’ve made to the console.
Why you should ever have to do this is something of a mystery to me, perhaps Microsoft just never expected anyone to decommission an Exchange server once it was built.