So I was going to install some plugins one morning, but InstallShield decided to hang. After some frustration, and a few days, I discovered that the .cab files were the culprit. I found this by double-clicking them, and PowerArchiver telling me that they were corrupt. I was dismayed that my favorite plugins were no longer available, but I have a backup. I had recently copied and installed these plugins to a different computer in January, and my backup (a separate drive) was from October, so no worries. I popped the drive in the dock, browsed to the folder, and, well, what do you know. I downloaded DataNumen's CAB repair program, which seemed to be the best option, since all roads were leading there. The trial version, which would at least tell you that the file could be repaired, failed. After some more research, and trying WinZip, WinRAR, 7zip, Windows extract, Total Commander, and maybe some others, the only bit of new information I got was that the header is corrupt. Now here's a real kicker... I opened explorer to c:\, and searched the entire computer for *.cab. It turns out that every data1.cab, _sys1.cab, and _user1.cab file on the entire computer does the same thing. My guess is that I don't actually have corrupt headers.