A more detailed error states:
Message: Access is denied
Have tried the following:
She logs in to this site from another PC - works fine
Coworker logs into this site from original user's PC - does not work
I log into this site from my PC - works fine.
So this appears to be a PC problem.
Have also tried: installing IE7 and various older versions of Java to no avail. Have even tried logging in to her PC with different XP profile but button still does not work.
User has full admin rights to her PC.