I have not done a Exchange 2010 install before, but from the error I am guessing at it having something to do with a User Account that it can not locate.
We get it - no one likes a content blocker. Take one extra minute and find out why we block content.
Not exactly the question you had in mind?
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If you install the account info dll, then this is visible via the users and computers snap-in, thru a new tab shown for user objects:
http://www.microsoft.com/downloads/details.aspx?FamilyID=7AF2E69C-91F3-4E63-8629-B999ADDE0B9E&displaylang=en
Hope this helps :)