DirSync "Coexistence MSI installation failed. msiexec returned 1603 Unable to uninstall the Microsoft Online Services Directory Synchronization tool."

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Not the best error message, I'll give you that.  Server management, add features, and enable .NET Framework 3.5.  Then install .NET 3.5 SP1 if you need it... but SP for .NET shouldn't be needed on Server 2008 R2.  Either way, DirSync install should work now.

Kthxbai.