Visual Studio Post build events

I want to maintain seperate config files for test and production like: web.config.Debug, web.config.Prod

I do have the actual config file as web.config

I am writing a post build event to copy the data from web.config.Debug to web.config when it is test or dev envirent (set in the Solution configuration drop down menu in the vs)

and I am copying the data from web.config.Prod to web.config when it is prod envirent (set in the Solution configuration drop down menu in the vs)

commandd used:

xcopy "$(ProjectDir)web.config.$(ConfigurationName)" "$(ProjectDir)Web.config" /y

I get error saying exited with code 4