Array to string conversion in rotating_banner_block_configure()

When navigating to the rotating banner block configuration page I get the following notice at the top of the page:

Notice: Array to string conversion in rotating_banner_block_configure() (line 648 of /home/site/public_html/sites/all/modules/rotating_banner/rotating_banner.module).

This appears to be the line:
'#suffix' => '<iframe id="rb-settings-nivo-effect-preview" class="iframepreview" src="http://files.megadrupal.com/rotating/nivo.php?fx='.$settings['nivo']['fx'].'"></iframe>',

It doesn't seem to prevent the module from functioning, but I do get a 502 bad gateway error if I try to select the camera(responsive) setting.