Disable Norton to dowload X3 and other plug ins?

Here's what I've done for years, and it has solved all of my corrupt DL and install problems:
 
- Use a reliable download manager (plenty of free ones out there) to download files.   I use DownThemAll, which is a free add-on to Firefox.  Do not disable antivirus for downloading, since it will catch anything questionable.
 
- When installing programs, always use "Run as Administrator".  When running (launching) programs, use "Run as Administrator".
 
- "Do" disable antivirus during installs.  Don't forget to re-enable it once finished.
 
- Reboot after installations.  Sometimes it'll ask you to, and sometimes not -- but it doesn't hurt to do it as a rule.
 
- Some folks like to compare checksums, though I've found that by following the above steps, it's never been necessary (It's also likely that my download manager is doing it "under the hood" anyway).

On the X3 download instructions web page, there are published MD5 hash values for each of the download files for X3.
 
After you complete the downloads, you can use any one of many freeware apps to determine the values for the downloaded files, and you can then compare those against the published values on the Cakewalk page, to make sure they match.  This guarantees that you downloaded everything properly.
 
Then, yes, it is recommended that you temporarily suspend or exit your antivirus software prior to installing Sonar.
 
In addition, I recommend you explicitly launch the installers with Run As Administrator set, to get the elevated privileges for a proper install.
 
I have had Avast interfere with the download process, so if you have corrupted download files, you may consider also suspending your antivirus during the downloads.
 
Bob Bone