In the code I gave you, the OID was lower-case "loop". In yours, it is upper-case "LOOP".
As for your last question (about listing the files in a directory), assuming you just want to list the files and not directories, you can use the following code (note, you would replace file:/c:/ with the full path to the directory you wish to list)
var choices = [];
var file = ogscript.getFile("file:/c:/");
if (file != null)
{
var subFiles = file.listFiles();
for (var i = 0; i < subFiles.length; i++)
{
if (!subFiles[i].isDirectory())
{
choices.push(subFiles[i].getName());
}
}
}
var constraint = params.createIntChoiceConstraint(choices);
params.replaceConstraint('Videos', constraint);#DashBoard