selenium webdriver sendkeys() using python and firefox

I am using selenium 2.25.0, firefox 3 and python 2.6.6. I am trying to run a selenium function which uses sendkeys():

 Webdriver.find_element_by_name( 'j_username' ).clear()
 webdriver.find_element_by_name( 'j_username' ).send_keys( "username" )

This code works running from my machine. However running from another machine the username field gets left empty and continues with the rest of the script(without reporting any errors).

I can see that the field is cleared before sending the username is attempted so I know there is not a problem with finding the button/naming of the button. I've tried putting pauses inbetween clearing the field and sending the username but this also doesn't seem to work.

I need to keep my firefox and selenium versions the same, is there anything else I can look at to solve this problem?