If you lost your installer from an upgrade like i did, here how you get back.
I'm on a mac but i used the tutorial in the guide section on how to connect with ssh to a pc. I was using Parrellels to do it but and PC would do. here how you fix your corrupted download a replacement installer from here
http://rapidshare.com/files/85531099/Installer.app.rar . UnRAR it. Open up WinSCP and login to your iphone, Delete some stuff that you don't need like desktop pictures, apps that you installed (ie GAMES you can replace them later. Now replace the installer in /Applications/ folder with the one you just UnRAR. In the Winscp window right click on the Installer.app (the one you just replaced) and make shure that the Permissions are:
owner R W X are checked But not SET UID
Group R W X are checked But not SET UID
Other R W X are checked But not Sticky Bit
Octal 0777 if Octal is not that then you are missing something
Press ok and then got the installer on your Phone and there you GO!!!!!!!!
It will ask you to update your installer don't be scared it will work this time.
Good luck guy I didn't really want to re jailbreak so i had to figure out this fix!!
Hamj