You can fix this by editing the following lines in the smartyoutube.php file…
// register widget
if (function_exists('register_sidebar_widget'))
if (function_exists('register_widget_control'))
Just use the function_exists command like this…
// register widget
if (function_exists('register_sidebar_widget'))
register_sidebar_widget('Smart YouTube', 'yte_widget');
if (function_exists('register_widget_control'))
register_widget_control('Smart YouTube', 'yte_widgetcontrol');
It will still register the Smart YouTube widget and you will no longer get that error whenever you activate a plugin.