xperf: error: NT Kernel Logger: Cannot create a file when that file already exists. (0xb7)
The error message is misleading and has nothing to do with a file that already exists. It happens when a different tool already started a NT Kernel Logger to capture ETW data.
Example of tools are Process Explorer (starting with Version 14), the Resource Monitor form Windows Vista/7 and Process hacker (with the extended tools plugin). All use ETW to capture Network and Disk IO statistics. This conflicts with xperf because xperf also captures ETW data. So before running xperf close those tools or disable disk/network IO tracing in the options of Process Hacker or use Process Explorer 12.04, which was the latest version without disk/network IO tracing.
I hope this helps you to fix the issue