Pushing package - error: package is being used by another process

One error we got quite often, but not always, btw: we are pushing packages during our TFS(xaml) builds, the build service runs as domain user:

Invoke NuGet push error: Failed to process request. 'There was an error processing the request: The process cannot access the file 'C:\ProgramData\ProGet\Packages.nugetv2\F1\Upper.MapProject.Newsletter.Module\Upper.MapProject.Newsletter.Module.1.6.nupkg' because it is being used by another process.'.

Invoke NuGet push error: The remote server returned an error: (500) Internal Server Error..

Any ideas?
Br

Any ideas we are pushing the packages via nuget.exe push…. so I don’t know which process is also using the file mentioned above.

Product: ProGet
Version: 4.5.3

This error means that another process is trying to access that file that is being uploaded. Most likely it's an anti-virus or search indexing program. Make sure to disable those on your Proget feed directories, otherwise this may happen frequently.

Antivirus is deactivated, I will try to disable SearchIndex as well, the interesting thing is that the package is uploaded successfully, so that seems quite strange to me.

br

Because we are using Windows Server 2012 R2 DataCenter Edition, SearchIndex wasn't even installed, but the error persists, any other ideas?

The only thing that will yield this message -- The process cannot access the file '...' because it is being used by another process. -- is another process having a lock on that file. Windows does not provide information about which process that is.

So, you'll need to use a tool like procmon to see file handles, and identify the culprit.