i have researched this the pass 2 days and i can't find a working solution to fix this. everything i try installing most of the apps comes up saying package download failed or main script execution failed....
Example, i try installing the youtube 1.1.4 activator "Main Scrtip Execution Failed!"
The two solutions I've had success with are trying to install a program and then hit the "clear queue" button. Reboot phone and try it again. The other method is to open installer, then hold down the home button for 10 seconds or so until it closes and then try again.
The other possibility is you're out of space and there's no room to download anymore stuff. Have you used bosstool to move your apps/ringtones/fonts? Or have you installed Cydia which does this for you? How many apps do you have installed currently?