There are many reasons why a PowerPoint presentation might not work on any given machine. We believe that it is often due to some difference in the version of PowerPoint it was created in, and the version on the machine on which it is to be presented. PowerPoint is PowerPoint you might argue, but it's not quite that straightforward. Could you name exactly which version of PowerPoint you have on your home PC/laptop? Which Operating System? Which Service pack? Maybe the answer is yes, but could you then answer the same questions about the computer in the Lecture Theatre you have been allocated ( At March 2006 you could reasonably hope to find Windows XP Pro version 5.1 SP2. and Ofiice PowerPoint 2003 SP1. ) Unless your presentation was created and maintained using exactly that set up you might have problems. The table below illustrates some of the versions of PowerPoint available - you might have created your presentation a few years ago using PowerPoint 98, then changed a few slides last year using PowerPoint 2000, and now you're trying to run it on PowerPoint 2003. Plenty of scope for problems to occur - and if there's a Mac in the equation, think again!
If you have (e.g) movies in your presentation they might not work even if the PowerPoint versions are identical - So remember the golden rule that you must always try your file on the actual machine you are going to use for your presentation.

Moving a presentation back and forth repeatedly between versions and/or between PC and Mac versions of PowerPoint will make your hair fall out. Small children will run away from you. Dogs will growl at you. And the world will generally not be your oyster. So don't.