Currently the server running Voice has a limit of 50mb for individual file uploads, so I imagine this is the problem!
You could try shrinking the file size down before uploading it. Your users may prefer it too if the file is smaller as it'll be faster to download and be less effort for computers to display.
There are some suggestions here on shrinking powerpoint files. I haven't specifically tried any but it could be worth investigating!
Joe - Voice Admin
That looks like the answer - pity the error message didn't suggest that file size was the problem. The file is all images so I think I will have to remove some of them, though I might try compressing them just in case.