error message (no replies)

Hi - I'm new here ... so please bear with me

I am getting this error message, I'm told to report it here ............
I have no idea what to do about it. Any help would be appreciated

Thank you
====================================

Notice: Undefined index: excluded_user_agents in /var/www/vhosts/xxxxxxx.net/site1/piwik/plugins/SitesManager/Controller.php on line 38

Backtrace -->

#0 Piwik_ErrorHandler(...) called at [/var/www/vhosts/xxxxxxx.net/site1/piwik/plugins/SitesManager/Controller.php:38]
#1 Piwik_SitesManager_Controller->index(...) called at [:]
#2 call_user_func_array(...) called at [/var/www/vhosts/xxxxxxx.net/site1/piwik/core/FrontController.php:125]
#3 Piwik_FrontController->dispatch(...) called at [/var/www/vhosts/xxxxxxx.net/site1/piwik/index.php:47]