On an SBS 2008 machine I was noticing the following error every day around 3:30 am
Event 2003, Perflib
The configuration information of the performance library
C:\Windows\system32\sqlctr90.dll for the
MSSQL$SBSMONITORING service does not match the trusted performance library information stored in the registry. The functions in this library will not be treated as trusted.
After much searching I came across a quite simple fix in the Technet library called Event ID 2003 — Performance Library Availability