Warning when saving pages

I have two exactly the same instances of wordpress (3.5) running. One is on my local drive using XAMPP and the other one is on a remote host. On a different remote host I have wordpress 3.4.2 with the latest version of the groups plugin.

On my local installation I can create/modify pages and save (publish/update) these without errors. However, when I do exactly the same on the remote host I get the following notices and warning.
The remote host running wordpress 3.4.2 doesn’t show these notices and warning.

Can you help me out on this one?

https://www.ads-software.com/extend/plugins/groups/