Specifically, this is for the failed updates that then refuse to update when you retry, often leading to a reinstall. When the client updates, it downloads all the files. Then, it unpacks and replaces each one, one at a time, deleting the old file. That's actually deleting the old file, not overwriting it. What will happen sometimes, is that the old file is deleted, but the new file doesn't go into place. If the old file is missing (or doesn't match, in some cases - like the legal method of editing the music file destination to play non-standard music), the client patcher comes to a screeching halt. To get past this blockage, either the old or new version of the file must be put into place in the client's folder. You can look at the patchlog file to see where it broke at (and typically, it's a good idea to get rid of the patchlog after a successful patch or two, to keep it short) There are two fixes for this: 1. Copy either version of the missing file from another install. For me, this happens to about every 3rd or 4th patch, but since I have 2 machines that I keep the game installed and up to date on, I can copy the offending file over my network into the folder (either the old or patched version). In my experience, even if two machines have this problem on the same patch, it is rarely the same file getting dropped in both, so you could update two machines, and one of them will patch past the point where the other failed, then you could replace that file, resume the patch, and hopefully get past where the first machine had its error, and repeat the process the other way. 2. After each patch, back up your client folder somewhere, then if this issue shows up, simply copy the one offending file back over and relaunch the client to continue with the update. Backing up these files (and your character data in My Documents) is never a bad idea.