error opening file => your file is not on the redirection server so client can not download it (and if your redirection server is a Linux one you may have a case problem so look for the web server error log and search for these files not downloading, and compare their real file name and the file name it tries to download, rename the real file name to match what client tries to download (there is surely in this case, an upper or lower case difference in the name)). If it takes a really long time to download it is surely because the file is sent directly by the game server and not the redirection server. Also I'm not sure but KF 2 server may not be able to redirect all mods files for client to download, I know there was problem just with custom maps which had a second package file (for example where textures and/or 3d models could be in), not sure if it is fixed now.