Helpers not working after moving from Xampp to Linux server

Check the filename. Is all characters are lowercase like array_helper.php ?

Looks like that was the issue - thanks!  It's weird - some of the examples I saw in various places involved naming the custom Helper files with capitalized first word, underscore, then lowercase "helper.php" (e.g. Example_helper.php), but then calling the file all lowercase in the controller like this:  helper(example);  I just changed the file names to all lowercase and the errors are gone.  I appreciate it!