Hello there,
First of all Id like to tell you I really appreciate this component. Wonderful work.
I have figured out everything about how it works (priviledges, categories etc). My only problem is this:

Warning: usort() expects parameter 1 to be array, null given in /public_html/xxxxxxxx/components/com_communitysurveys/models/survey.php on line 3417

This line is repeated 10 times, but everything seems to be up and running.

Any idea about how to solve this?

Thank you in advance