When creating a marketing plan, users have the option to set up segment summaries with packages in their planned marketing efforts. However, when a marketing effort is created from one of these plans, and then users attempt to add segment groups to the segment summaries, they will receive the error:
Object reference not set to an instance of an object.
This only occurs when the segment summaries are assigned packages in the marketing plan.
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.