We are attempting to create a package as well and have received the same result, but we do not have the vendor unattend install script. Can you post the script? What version are you trying to install? Also, have you tried creating a batch file using the command line syntax and then create a bat file distribution package?
If a reboot is being triggered from the install then you need to pass LANDesk an exit code to tell it that the install is fine and has performed correctly. I've used the following in a batch file in the past.
IF “%ERRORLEVEL%”==”3010” EXIT /B 0
IF "%ERRORLEVEL%"=="1" EXIT /B 0
This will run the executable file along with any command line parameters. Exit code 3010 and 1 are classic exit codes from Install Shield installers which indicate a successful install or a reboot required.