Dept. of Non-obviousness: Drupal configuration message

You might not think that this stream of messages would be caused by character encoding:

Notice: Undefined index: highlighted in include() (line 126 of C:wampwwwdrupal-7.22modulessystempage.tpl.php). Notice: Trying to get property of non-object in drupal_alter() (line 1042 of

I was editing a configuration file and switched to UTF-8 because I needed to add a few unusual characters to a web page. When I did so, the stream of errors appeared. It took a long time of searching before I discovered. this discussion page where ANSI vs. UTF-8 was mentioned.
It’s not a universal law, but experience shows that the bigger the gusher of error messages, the cause is usually quite small and and the least obvious.