Microsoft Office 2003 for MAC typing problem

We currently use Microsoft Office 2003 Suite on MAC OS X. A couple of users have started noticing that when using Powerpoint, Word, and Excel that we cannot use any key on the keyboard. It happens randomly. We have to click out of the application with our mouse and then click back and the keyboard works again. It does not happen in any other application. It happens as much as every 30 seconds while working in a document sometimes. It’s very frustrating! Has anyone encountered this?