what does OSStatus error -49 mean?

I'm trying to export a slideshow in iphoto '09

"Display" resolution (highest of the choicse)

I get this error about 75% of the way through

OSStatus error -49

Did a google search and someone suggested to change your energy settings to "Sleep - Never". I did that and still get the error.

It takes about 60 minutes of exporting to get to the point where the error happens so it is pretty time consuming to "test"