Give us a lot more details.
Exactly what do you see happen? What is the complete exact unedited word-for-word error message?
How many images are you exporting?
What is the version NUMBER of Lightroom? What operating system?
My notebook has completely crashed when I export my photos. I am only exporting 1! I think the version is 7. The system is windows
In the postprocessing section of the export module, make sure you have selected, "Do nothing". Don't know if that's your problem, but it's something to look at.