> - we extract a zip archive to provide an initial setup for Plopp data
> - then the user can play around in demo mode (problem doesn't occur in a
> full version as the deletion doesn't take place)
> - upon quitting demo mode all data is erased via a recursive directory
> delete
> 
> 
> We have simple test up without running the UI to reproduce the problem.
> 
> The delete fails about 1 in 10 with a primitive failed in deleteDirectory.
> 
> There are no open files or anything obvious.

That's a fairly common problem with file deletion on Windows. On a
typical installation, there *are* often open files - the usual
suspects are a virus scanners and file system indexers/search engines;
the explorer may also open files if the directory is display in the
explorer.
They register for file change notifications, and when files are created,
they put them onto their todo list, and will eventually open them
(usually fairly quickly after they got created). They then read them
once, and deletion attempts will fail at that point.

If that's the cause, it is fairly difficult to work-around. The "proper"
way is first to try DeleteFile (talking plain Win32 API here); if that
fails with sharing violation, move the file to the trash folder, open
it for deletion, SetFileInformation with a delete disposition, and close
the file. In the latter case, the file will go away if the last handle
is closed.

If you wait some time and retry, whoever had the file open will have
closed it.

Regards,
Martin