iexplorer error 1400

I have a windows 2000 pc. When my employee logs on to the internet, she gets an iexplorer system error code: 1400 Invalid window handle error. When she closes out of the error, advertisements pop up. It seems to disable her popup blocker. She is running ie 6.0.

I have checked the microsoft and internet explorer web sites looking for the error code but nothing pops up.

Any ideas

Thanks