Plugin Conflict

Hi,
I am trying to use a conditional menu item plugin called “If Menu” to show/hide menu items depending on a users logged in state. . . .

It is throwing the following error:
Warning: Missing argument 2 for rc_sweet_custom_menu::rc_scm_edit_walker() in /home/czucker/public_html/wp-content/themes/HighendWP/admin/custom-walker/sweet-custom-menu.php on line 90

Something hard coded into the theme also seems to be removing the menu item visibility option. . . .

Is there a possible workaround?

Thanks for all of the great support,
Chris