innerHTML Question

[javarunner]

This is obviously not a direct Ajax question, but thought someone would be able to help since it's a common action in Ajax-based pages.
My page contains a 'div' tag like <div id='foo'></div>
In my script I get a handle to this tag by:
var foobar = document.getElementById("foo");
When I reference it as:
foobar.innerHTML = options;
where options contains a value which I've built in my script. I can display it in an alert right before the getElementById.
I get an exception that says foobar has no properties.
Does anyone know why?
TIA...