Scenario:
Exchange 2010 EMC works fine until a day when you launch it and get the error as shown below:

There are 2 steps to fix this and a workaround to troubleshoot further.
Solution:
Step 1 is to open up the registry and navigate to the following key:
- HKCU\Software\Microsoft\Exchangeserver\v14\AdminTools\NodeStructureSettings
Under the NodeStructureSettings key delete the value NodeStructureSettings (shown below)

Step 2 is to remove the cached information under the user directory:
- C:\Users\<Username>\AppData\Roaming\Microsoft\MMC

After you have completed these 2 steps then try launch the EMC again. If it still fails you can continue to the workaround and carry on troubleshooting.
Workaround:
Launch the EMC again and click on Microsoft Exchange in the top left hand corner. You will see an option “Add Exchange Forest…”, click on this, a new window will appear.
Enter in a name and then under the url you can enter the following:
- http://FQDN ServerName/PowerShell
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Once you click the OK button you can now click on the name you just gave and you should see the following:

The EMC is now getting all the information for the current user. Once done you should be able to browse the EMC like before:

Hope it helps.