Very recently a customer did an upgrade from v8.1.0 to v8.1.1 which falied with the following error
Error installing packages: TSWGenericError: Anotherinstall or uninstall is already occuring, wait until it has finished and tryagain"
Very wierd we though, looked through the McAfee KB and nothing but after more research found that during an upgrade or patch application a pack.lock file is created to lock out any other patch from running.
Usually this file is deleted after the patch is completed, but in this case no. So to fix this see below
Login to the console
cd to /var/packages
ls to find pack.lock
then apply the next patch
Hope this helps