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After installing .NET 4.5 you are not able to access performance data using WMI. For example, when you try to get the value for the Win32_PerfFormattedData_ASPNET_ASPNETApplications performance counter, the value returned using WMI is always 0.
This is by design as a security fix. Only admin and performance log/monitor can access asp.net performance information.
Infelizmente, ainda não encontrei uma maneira de fazer isso funcionar.