This is the technical support forum for Toolset - a suite of plugins for developing WordPress sites without writing PHP.
Everyone can read this forum, but only Toolset clients can post in it. Toolset support works 6 days per week, 19 hours per day.
The issue here is that the user is not able to select Posts to add to his post groups in the Access plugin.
Usually cases like these are caused by plugin conflicts and as such I would recommend that you temporarily disable all your non-toolset plugins and try again.