It means what it says. It will also tell you what file it is failing for, in the last dialog.
Usually it has to do with an anti-xxxx program causing the patcher to not be able to patch a file. We know of, at least, four anti-xxxx programs which have been corrupting patches.
The failure could be any one of the other executables in the folder.
The error is real. Once you get it, you pretty much have to do a full installation in order to fix it.
