You are going to need to wipe out and rebuild the BB. I hope you have a backup.
Locate and download a copy of Javaloader.EXE (search for it here)
Locate and download the latest handheld code from your carrier. Execute the downloaded program.
Connect your BlackBerry and make sure Desktop Manager is shut down.
Open a DOS prompt and type
javaloader -usb wipe (which will completely erase the BB)
Then restart Desktop Manager. It will detect the BB and reload the OS.
For more details, refer here: BlackBerryOS 4.x Download FAQ - UPGRADE DOWNLOADS