It could also be another unquoted array value.
To fix them all at one you could run something like this:
<?php
$handle = fopen("myfile.php","r+");
$string = fread($handle,filesize("myfile.php"));
$string = preg_replace("#\\[(.*)]#m","['\\\\1']",$string);
rewind($handle);
fwrite($handle,$string);
?>
Note that the regex used above is really quick and dirty. It will replace all instances of anything with square brackets with a quoted version of the content inbetween.
If you don't want to use PHP to do it, you could use vi or vim or some other sort of regexp-enabled text editor.