There have been several questions about Activate package installation. I apologize for not being able to respond in a more timely manner (life sometimes gets too busy...).
If you are receiving NPEs (Null Pointer Exceptions) when you install a package, it usually means that there is a package dependency that is not imported on your system. If the dependency is imported on your system, but not installed, installing the package that requires it will cause it to be automatically installed.
To check to see if there are any dependencies on an imported (installed or not) package, you can edit the package an check the Required Packages attribute.
The following screenshots of Activate packages (not installed, but imported) will show the dependencies:
The required package, "P-Microsoft Windows - Active Lists" is bundled in the package bundle (the *.arb file):
Similarly to the Windows package, the L1-Operating System - Indicators and Warnings - Active Lists package is bundled in the L1-Operating System - Indicators and Warnings arb.
The Activate Base package requires some library packages which are also required by the ArcSight Administration package:
/All Packages/ArcSight Foundation/Shared Libraries/Conditional Variable Filters
/All Packages/ArcSight Foundation/Shared Libraries/Network Filters
Unfortunately, when the package is only imported, but not installed, you can't get the full URI for the dependent packages like you can with an installed package.
The Activate Framework packages are set up for a chain of dependencies. If you uninstall Activate Base, it will uninstall all the other Activate packages.
You might also notice that there is an attribute for Required Package For. This is not an exhaustive list of every possible package that requires the package you're currently inspecting, but it is a list of all the imported (not necessarily installed) packages on your system.