During a recent migration from SBS2003 to SBS2011 I received this error:

Screenshot - 08_10_2013 , 13_40_14

Access Control List (ACL) inheritance is blocked.

This is a permission issue in Exchange whereby the permissions need to be able to propagate to the child objects. In my case, to enable this please follow these steps:

You’re going to need access to the Security Tab in Exchange System Manager which typically by Default isn’t enabled for security reasons. You can re-enable this through the registry:

Phase 1
Click on the Start button and Run –  In this box type regedit and click open.

In the window that opens you’ll need to navigate to the following folder (Key): HKEY_CURRENT_USER\Software\Microsoft\Exchange\EXAdmin

Screenshot - 08_10_2013 , 14_43_20

Right click on the right pane, go to New and then DWORD Value
In the new value that shows type in ShowSecurityPage then double click it and in the data area change this from 0 to 1

Now you will be able to see the security tab in Phase 2

Phase 2
Open Exchange System Manager, expand the Exchange Server and then the Storage Group.

Right Click on the Mailbox Store (you may have more than one) and go to ‘Properties’.  Click on the ‘Security’ Tab at the top then ‘Advanced’ nearer the bottom. On the Window that pops up you should see ‘Allow inheritable permissions from the parent to propagate to this object and all child objects’ –  Tick this box and click Apply & Ok.

Screenshot - 08_10_2013 , 14_01_32

Now you can go back to the migration wizard and click Scan again, the error now shouldn’t appear.
(MS say that you should restart your Server, however I didn’t need to)

Hope this gets you out of a sticky quibble.