Also Review our .NET Performance Metrics documentation.
If you have installed or recently updated your .NET agent to 8.20.262.0 or above you may have encountered this error or one similar:
The executing user, IIS APPPOOL\DefaultAppPool, has insufficient permissions to collect Windows Performance Counters.
This error is indicating that the user your application is running under does not have the permission to access the Performance counter data. This should not affect the operation of the agent, but it will prevent the agent from collecting the new Performance Metrics that were recently introduced in our .NET Agent 8.20.262.0 release.
If you want to access those metrics, you’ll need to grant your IIS user access to the performance counter data in Windows.
For .NET Framework applications, the Windows User under which your application runs must have access to Windows performance counter data. Usually this is accomplished by adding the user to "Performance Monitor Users" and "Performance Log Users" groups. Insufficient permissions will result in the agent not collecting garbage collection metrics.
If you do not wish to grant your IIS user access to the performance counter data in Windows, it does not impact the .NET Agent’s ability to monitor your application’s performance.
Note: If you have granted your user permissions and are getting this error:
System.Exception: Unable to obtain current process' instance name for category .NET CLR Memory when trying to build counter
It could be that some performance counters on your box are corrupted or missing. Here is an article from Microsoft on enabling/rebuilding the counters to resolve that error: How to manually rebuild Performance Counters for Windows Server 2008 64bit or Windows Server 2008 R2 systems