[jQuery] setting focus on input text field

I am struggling with setting focus on an input text element. I have 2
input text elements as follows:

<fieldset id='rackScanEntry'>
RU:<input type='text' size="2" id='ru'>
Barcode:<input type='text' name="assetBarcode" size="20"
id='assetBarcode'>
</fieldset>

the first is usually updated by js using val() jquery method. Then I
have a "change" event on the second one. Once change is triggered, the
values of the two elements are validated and then stored in an array
for an ajax post later. I then increment the value of the first field
and then set the value of the second to empty using val("). Finally, I
try to reset the focus on the second field to wait for another entry.
No matter where I put the $("#assetBarcode").focus() code, I can not
get this to focus. What am I doing wrong? Thanks for your help.