Similar to this post , I get the same error.

Selecting a different Group Administrator generates this error:
Fatal error: Call to a member function load() on a non-object in /.../.../public_html/administrator/components/com_community/controllers/groups.php on line 439

Hi Jason,

administrator access detail is not valid. please check it again. I need that for debugging purpose

Regards,
Albert

drat.

Please try again, that login is now an administrator.

Hi Jason,

could you please upgrade to jomsocial latest version 3.2.1.4? you can do it from ijoomla installer or download from jomsocial.com "My Account"
If you don't want because some reasons, you can provide me FTP access detail. your FTP access detail seem wrong user, because when I logged in I only got empty folder.

Regards,
Albert

My bad, didn't read the wizard when creating the FTP account. It should work now. Please go a head an update the version, I've made my backup.

Hi Jason,

this is old bug. but I already put the fixes for you. /administrator/components/com_community/controllers/groups.php line 437:
from

$member	= JTable::getInstance( 'GroupMembers' , 'CommunityTable' );

$member	= JTable::getInstance( 'GroupMembers' , 'CTable' );

Hi Jason,

We have not received any response back from you in over 7 days, and would like to know if you consider this issue to be resolved. If you have any further questions, simply reply to this post.

Regards,
Albert