Why does xcopy exit with code 9009 in Visual Studio post-build step?

I encounted this error on the TeamCity build server. I finally resolved it after checking the build log and found:

“‘xcopy’ is not recognized as an internal or external command.”

I then changed my statement to:

C:\Windows\System32\xcopy “$(ProjectDir)config\Web.config.$(ConfigurationName)” “$(ProjectDir)Web.config” /Y/R