After installing internet explorer 9, the following error may appear “You must close all dialog boxes before you can close Exchange Management Console”.

Reviewing Microsoft web site didn’t provided  any solution for this issue (although it looks like a commutability issue between Exchange 2010 and Internet Explorer 9).

Currently there is  a few workarounds that may use:

1. Uninstall Internet Explorer 9 (I usually don’t recommended to uninstall applications from a production server, so do it on your own risk).

2. Add https://localhost ”  and ” http://localhost  as a Trusted Web Sites (Under Internet Explorer –> Security –> Trusted Sites).

3. Created a customized MMC and add to it Exchange 2010 Snap-in.

4. Wait for Microsoft official solution/hotfix.