Most likely your groups have a blank value in them.
it is very easy to add a group member with a blank value and not see it.
Open the Security Assist Access Groups manager and edit each group that you have created.
try to click bellow the last group member to see if there is a blank group member.
If you can select a line with nothing in it bellow the last group member there is a blank one. remove each of the blank group members you find.
the easiest way to see if there is a blank group member or not is directly in the WA_SecurityAssist/HelperGroupsRulesPHP.php file.