À uns dias num projeto que tenho, estava a analisar erros de SCOM relacionados com IIS's e tive de pesquisar e acabei por encontrar este link abaixo.
Dei grants conforme indicado e deixou de ocorrer.


Event ID 2289 — IIS Worker Process Tracing
http://technet.microsoft.com/en-us/library/cc735142(v=ws.10).aspx

Event ID 2289 — IIS Worker Process Tracing

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Updated: January 20, 2010
Applies To: Windows Server 2008

In Internet Information Services (IIS) 7.0, worker processes can trace request activity. Of the requests that reach the worker process, you can log successful requests, failed requests, or all requests. In order to log this information, the worker process identity must have permissions to create directories and subdirectories, and to write files to the directory configured for the site.

Event Details

Product:	Internet Information Services
ID:	2289
Source:	Microsoft-Windows-IIS-W3SVC-WP
Version:	7.0
Symbolic Name:	W3_EVENT_FAILED_TO_DELETE_FREB_FILE
Message:	FailedRequestTracing Module failed to delete at least one log file from the directory '%3'. The problem happened at least %1 times in the last %2 minutes. The data is the error.