This can caused by a permissions issue when the installer attempts to copy fonts between FSX and the Windows OS fonts folder.
To solve the issue manually:
We've also recieved word that this issue can be caused by disabling the "Distributed Link Tracking Client" service, which is recommended by many popular "tweaking" guides. We highly discourage any disabling of Windows services. The performance gain is negligible at best and at worst you run the risk of causing strange issues such as this one.
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