My ExtJS combobox that was working with Firefox was showing this error message on IE8. The reason for this was a trailing comma in my Javascript matrix.

My data store was like this:

var shopList= [
    ['702038', 'some dude name'],
    ['1120685', 'another dude'],
];

Ok, it’s a stupid mistake, but it can happen when you delete the last option and forget to remove the comma. A way to avoid this types of mistakes is using an IDE such as Netbeans that will signal you the error immediately with a graphical hint. After removing the trailing comma it worked in IE too:

var shopList= [
    ['702038', 'some dude name'],
    ['1120685', 'another dude']
];