[c#] What is going wrong when Visual Studio tells me "xcopy exited with code 4"

I'm not very familiar with post-build events, so I'm a little confused as to what's going wrong with my program. When compiling in visual studio 2010, I get the following:

The command "xcopy C:\Users\Me\Path\Foo.bar\Library\dsoframer.ocx C:\Users\Me\Path\Foo.bar\bin\Debug\ /Y /E /D
xcopy C:\Users\Me\Path\Foo.bar\ApplicationFiles C:\Users\Me\Path\Foo.bar\bin\Debug\ /Y /E /D
xcopy C:\Users\Me\Path\url\ C:\Users\Me\Path\Foo.bar\bin\Debug\ /Y /E /D
rmdir /S /Q C:\Users\Me\Path\Foo.bar\bin\Debug\.gwt-tmp" exited with code 4.    

The program appears to run fine, despite this error, but I don't want to just ignore this issue and hope nothing bad happens. Strangely, this line started out as only a single command (the first xcopy) but as I continued to compile the project (fixing other problems, mostly references) the error message expanded larger and larger. Any idea what could be going on?

Edit: Here are the postbuild events that seem to be failing --

xcopy $(ProjectDir)Library\dsoframer.ocx $(TargetDir) /Y /E /D
xcopy $(ProjectDir)ApplicationFiles $(TargetDir) /Y /E /D
xcopy $(SolutionDir)com.myUrl.gwt\www $(TargetDir) /Y /E /D
rmdir /S /Q $(TargetDir).gwt-tmp

I addition to the accepted answer, the error can also occur when the destination folder is read-only (Common when using TFS)

If any other solution is in the debug mode then first stop them all and after that restart the visual studio. It worked for me.

I had a post build command that worked just fine before I did an update on VS 2017. It turned out that the SDK tools updated and were under a new path so it couldn't find the tool I was using to sign my assemblies.

This changed from this....

call "%VS140COMNTOOLS%vsvars32"
    "C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6 Tools\x64\sn.exe" -Ra "$(TargetPath)" "$(ProjectDir)Key.snk"

To This...

"C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools\x64\sn.exe" -Ra "$(TargetPath)" "$(ProjectDir)Key.snk"

Very subtle but breaking change, so check your paths after an update if you see this error.

As other answers explain, exit code 4 may have many causes.

I noticed a case, where resulting path names exceeded the maximum allowed length (just like here).

I have replaced xcopy by robocopy for the affected post build event; robocopy seems to handle paths slightly different and was able to complete the copy task that xcopy was unable to handle.

In my case the issue was due to incorrect build order. One project had an xcopy command on post-build events to copy files from bin folder to another folder. But because of incorrect dependencies new files were getting created in bin folder while xcopy is in progress.

In VS right click on the project where you have post-build events. Go to Build Dependencies > Project Dependencies and make sure its correct. Verify the project build order(next tab to dependencies) as well.

I had the same problem. You could also check which way the slash is pointing. For me it worked to use backslash, instead of forward slash. Example

xcopy /s /y "C:\SFML\bin\*.dll" "$(OutDir)"

Instead of:

xcopy /s /y "C:/SFML/bin/*.dll" "$(OutDir)"

I got this along with the message

Invalid drive specification

when copying to a network share without specifying the drive name, e.g.

xcopy . \\localhost

where

xcopy . \\localhost\share

was expected

It means:

Initialization error occurred. There is not enough memory or disk space, or you entered an invalid drive name or invalid syntax on the command line.

So basically it could be just about anything haha...try running the command one at a time from the command prompt to figure out which part of which command is giving you trouble.

This error is due to if there is white spaces where your repo is copied. E.g. my project is copied in below location c://projects/My rest project then you can see the white spaces there, if you change your repo path to below, it should work c://projects/myrestproject

I ran across this issue, so I ran the xcopy command from the command line and it said:

File creation error - The requested operation cannot be performed on a file with
 a user-mapped section open.

It was actually Visual Studio holding onto something. I just restarted Visual Studio and it worked.

Switch the watch tab to the "ouput" and look for the xcopy command. Sometimes here you find some more message ( the actual xcopy output ) that could help you to solve the issue. If you don't see the output tab, use View-Output menu to show it.

Another thing to watch out for is double backslashes, since xcopy does not tolerate them in the input path parameter (but it does tolerate them in the output path...).

This can also come if the target folder is used by some other processes. Close all the programs which may use the target folder and try.

You may use resource monitor(windows tool) to check the processes which uses your target folder.

This worked for me!.

If source file not found xcopy returns error code 4 also.

I received the 'exited with code 4' error when the xcopy command tried to overwrite a readonly file. I managed to solve this problem by adding /R to the xcopy command. The /R indicates read only files should be overwritten

old command:

XCOPY /E /Y "$(ProjectDir)source file" "destination"

new command

XCOPY /E /Y /R "$(ProjectDir)source file" "destination"