Portable Prezi works on OSX but not Windows

Hi

We've created a presentation and when downloaded as a portable prezi it works without any problems on Mac OSX but on every PC we've tried it fails to open - it says 'this make take a few minutes' and then you get the 'program is not responding' error.

The file name is short (which seems to be one common issue with Windows). There are no YouTube videos. The image sizes aren't massive, or the videos. The PCs have been running Windows 7.

Any ideas?

cheers
Tom