I am not certain from the thread whether you tried this series of steps:
Access the affected computer either directly or via a remote control product.
Launch the portal and manage that client's computer.
Now, run the fix on the affected computer.
For some reason known only to Symantec, FIX doesn't work remotely all the time - and I'm guessing here - no one has ever contacted Support to log the issue so that it can be investigated.
If you followed the above steps and it still doesn't work, please call 866-807-6047, option 1, option 4, option 1 and get them to take a look.
Hope that helps!