I have the same problem.  The update didn't work and I tried holding the shift key when launching, but still didn't work.  I am a new Mac user and don't know my way round the operating system like windows.

I am trying a reinstall of Autocad with the update again to see if this works, otherwise I have an iMac with a Version of Autocad that is unusable....  (not a dig at the people trying to help, just frustrated)