This occurs if there are two concurrent calls to retrieve information from the same ESX/ESXi host.
You may want to reference the VMware KB listed below.
I was able to locate similar text in my logs when we were experiencing an 'Access Violation'. The output is below. KB 2050700 helped resolve.
mem> -->
mem> [25904 verbose 'Locale' opID=6fe4f279] Default resource used for 'EsxHostAdvSettings.UserVars.CIMemc_sehostProviderEnabled.summary' expected in module 'option'.
mem> [25904 warning 'Locale' opID=6fe4f279] No message string to format object vim.option.OptionDef.
mem> -->