Hi,
It looks like this function only works if the owner of the object has the necessary abilities on that estate (which makes sense), and is online. It stops working a short while after the owner logs off, and does not work at all on group owned land if the object is deeded to the group.
It would be good to know if that's how it's intended to work, or if it will be changed/fixed to work on group owned land when deeded to the group, or if the owner is offline. One possible application of this function is an object in a rental unit, that the tenant can use to determine his/her prim count on that parcel. Currently, there is no way to create such an object, the script stops working once the object owner logs off.
More info in this thread:
/54/1e/152006/1.html
Thanks,
Ziggy