I just installed this plugin and I get the exact same error.
One thing that I did note – it actually does seem to save the settings if I click Back… except if I try to change the Ignore Users fields. My Analytics Profile information and any of the selected check boxes are saved – just not the Ignore Users entries. Editors was the default entry and I also added Administrators. Now no entries appear in that field.
I also disabled caching, but to no avail.